The Study of Metaphor in Argumentation Theory

This paper offers a review of the argumentation-theoretical literature on metaphor in argumentative discourse. Two methodologies are combined: the pragma-dialectical theory is used to study the argumentative functions attributed to metaphor, and distinctions made in metaphor theory and the three-dimensional model of metaphor are used to compare the conceptions of metaphor taken as starting point in the reviewed literature. An overview is provided of all types of metaphors distinguished and their possible argumentative functions. The study reveals that not all possible argumentative functions of metaphor have been taken into account, such as the role of conventional direct metaphors in standpoint and starting point. Novel direct metaphor as part of an analogy argument has received most attention, while indirect metaphor can constitute argumentative moves as well, such as the introduction of a standpoint, starting point or connection premise. The overview also shows that certain combinations of variables seem to be impossible of unlikely to occur. These results have a bearing on the analysis of metaphors in argumentative discourse and show the omission in current studies of metaphor. Being aware of these dimensions of metaphor ánd of its potential in argumentation would enrich argumentation studies and metaphor studies alike.


Introduction
In several speeches in 2016, then United States Secretary of Defense Ashton Carter discussed the US approach to ISIS (or ISIL), the jihadist militant group in Iraq and Syria. In these speeches, Carter used various metaphors, such as the TERRORISM is CANCER metaphor. The following is an excerpt of a speech Carter gave at Fort Campbell, Ky., in January 2016 to troops that were being sent to Iraq.
(1) ISIL's a cancer that's threatening to spread. Like all cancers, you can't cure the disease just by cutting out the tumor. You have to eliminate it wherever it has spread and stop it from coming back. (Carter 2016) The expression 'ISIL's a cancer' is a metaphor that invites a cross-domain mapping between the domains of terrorism and cancer. This metaphor seems to have an argumentative purpose: Carter uses the 'A is B' construction to draw an analogy between cancer and ISIS to justify the White House's military strategy. In the same week, Carter used the same metaphor with a different linguistic expression at a news conference in Paris. There, he states that the main objective in the war against ISIS should be "to destroy the ISIL cancer's parent tumor in Iraq and Syria by collapsing its two power centers in Raqqa and Mosul." In addition, he uses another metaphor as he employs the term 'collapsing' when speaking of the power centers in Raqqa and Mosul: the more basic or concrete meaning of collapsing is 'if a building or other structure suddenly falls down', but Carter uses it here to indirectly express 'to suddenly fail or stop existing' (MacMillan online dictionary). This last use of metaphor has a different linguistic presentation and also seems more conventional than the first 'tumor'-metaphor. Yet it is unclear how the argumentative function of these metaphors should be determined. So, although each of these examples (ISIL's a cancer', 'ISIL cancer's tumor' and 'collapsing') can be considered as an instance of metaphor, they differ on three parameters: they have a different linguistic presentation, they have different levels of conventionality, and they might also have different communicative functions in the discourse. Metaphors that differ on these parameters may impact everyday argumentative interactions differently.
Which expressions are considered metaphorical and which metaphors are considered argumentative depends on one's view on metaphor and argumentation. In the current argumentation-theoretical literature, not much attention is given to different types of metaphor, even though this variety of metaphor is part of language users' reality. To get a grip on metaphor in argumentative discourse, scholars would need to combine insights from metaphor theory and from argumentation theory. Although there is a vast amount of literature in both fields, they do not commonly combine their approaches. Metaphor research offers a cognitive approach to metaphor and distinguishes various instantiations of metaphor often disregarded in argumentation theoretical studies, while such cognitive-linguistic research does not particularly take into account the conceptual distinctions posited in argumentation studies. This paper offers a review of the 1 3 The Study of Metaphor in Argumentation Theory argumentation-theoretical literature on metaphor in argumentative discourse. By making explicit which starting points fuel the views and analyses in these studies, they can be systematically compared and a more complete overview of metaphor in argumentative discourse can be provided. It intends to lay bare the omissions in the literature and fills these with additional real-life examples of various metaphors.
This review is organized by combining two methodologies: the pragma-dialectical theory of argumentation Grootendorst 1984, 2004) and metaphor theory (Lakoff and Johnson 1980;Steen 2008). Pragma-dialectics is used to study the argumentative functions ascribed to metaphor as it offers a framework and terminology to differentiate between possible moves in argumentative discourse. Distinctions made in metaphor theory are used to compare the conceptions of metaphor taken as a starting point in the reviewed literature.
Ultimately, the variables extracted from these methodologies (argumentative functions and types of metaphors) are crossed and result in an overview of all types of metaphors distinguished and their possible argumentative functions. The two methodologies are introduced in Sect. 2. Then, Sect. 3 expounds the conceptions of metaphor described in the argumentation-theoretical literature. To limit the scope of this study, only literature with an argumentation theoretical perspective focusing on verbal metaphor is considered. Section 4 compares the argumentative functions ascribed to metaphor in the reviewed literature and Sect. 5 discusses the results of that comparison. Section 6 contains the conclusions about what views on metaphor are taken in the argumentation-theoretical literature and what implications this has for the actual and potential attribution of argumentative functions to metaphor.

Argumentative Functions
In order to compare different approaches to the function of metaphor, I will apply argumentation-theoretical concepts, using terminology stemming from the pragmadialectical theory of argumentation Grootendorst 1984, 2004). Pragma-dialectics is a suitable framework for specifying the functions of discourse elements, because it offers an overview of all the moves in a critical discussion, enabling the analysis of argumentative discourse in terms of these moves (van Eemeren and Grootendorst 1984: 98-105).
The most prominent moves in a discussion are advancing a standpoint and advancing arguments, and these are based on certain introduced starting points. In pragma-dialectics, a single argument consists of a standpoint and a material premise (or minor premise) which is connected to the standpoint with a connection premise (or bridging/maior premise). The connection premise represents the relation between argument and standpoint, the argument scheme that justifies the transference of acceptability from premise to conclusion. This transference is based on a particular relation between what is stated in the standpoint and what is stated in the argument, for instance a causal relation, an analogy relation or a symptomatic relation. For example, a single argument based on an analogy relation can consist of a standpoint 'This method will work for this problem', supported with the argument 'because it worked last year', which are connected by the premise 'and this problem is similar to the problem we had last year' (van Eemeren and Grootendorst 1992: 97-98). Each premise of the argument can itself be further supported with argumentation. When this happens, the premise turns into a substandpoint, as this premise is, or is considered to be, disputed as well.
To ensure that a standpoint is accepted by the audience, discussants should make use of shared starting points in their argumentation, also known as points of departure or mutual concessions. Pragma-dialectics distinguishes material and procedural starting points. Material starting points include shared facts and values which function as a point of departure for a discussion about a standpoint. Procedural starting points constitute the agreements on how the discussion is to be conducted, e.g., which types of arguments are allowed or how discussants take turns (van Eemeren and Grootendorst 1992: 93-94; van Eemeren 2010, p. 44).
To limit the scope of this review, I will focus on the use of metaphor as (part of) three moves: advancing a standpoint, advancing argumentation, and introducing starting points. These are the moves that imply commitment to a certain propositional content and they constitute the actual argumentation in a discussion. Argumentation-theoretical literature discussing actual discourse therefore generally focuses on these discussion moves. In the pragma-dialectical model of a critical discussion, other moves are distinguished as well, such as accepting a standpoint, expressing doubt, and requesting argumentation, but these do not introduce commitments as the three mostly discussed moves do.

Types of Metaphor
Apart from the possible argumentative functions, one needs to distinguish the kinds of metaphor that may be taken into account in the reviewed literature. Some literature may only address certain manifestations of metaphor while ignoring other kinds. A broad perspective of metaphor prevents that certain kinds of metaphor are overlooked.
In traditional conceptions of metaphor, originating in Aristotle's writings, metaphor is generally seen as a stylistic feature that manifests itself in language. In this article, the three-dimensional model of metaphor is adopted (Steen 2008(Steen , 2011, which views metaphor as a cross-domain mapping, not only on the level of language, but also on the level of thought and communication. This approach takes a very broad conception of metaphor as its starting point, incorporating metaphors in our mental conceptualization of the world, direct metaphorical comparisons and similes, and indirect metaphors in language consisting of a single word. The 3D-model is mainly based on Lakoff and Johnson's (1980) conceptual metaphor theory (CMT) which posits that metaphor is a cross-domain mapping in thought, connecting an abstract domain with a more concrete one (e.g., Kövecses 2010;Gibbs 2011). The theory argues that our everyday thinking and talking is full of metaphor, for example when we think about the concept of soccer (the so-called 1 3 The Study of Metaphor in Argumentation Theory target domain) in terms of war (the source domain), and view the opposing soccer team as 'the enemy'. These conceptual structures are (automatically) reflected in all kinds of linguistic expressions, thus shaping the way we speak and act when it comes to soccer. In addition, Steen (2008Steen ( , 2011 distinguishes a third, communicative dimension of metaphor, addressing the goal-oriented use of metaphor in interaction between language users. 1 On each of these three dimensions, different kinds of metaphors can be distinguished. These distinctions help to put the accounts of metaphor in the argumentation-theoretical literature into perspective. To identify metaphors in language, MIPVU, a metaphor identification procedure, was developed (Pragglejaz Group 2007;Steen et al. 2010a, b). According to MIPVU, a word is considered metaphor-related if its contextual meaning differs sufficiently from the more basic meaning of the word, and if the contextual meaning can be related to the basic one based on some kind of similarity (Steen et al. 2010a, b). The procedure also distinguishes between indirect and direct metaphors. The fragment 'ISIL's a cancer' in (1) contains an indirect metaphor: the basic meaning of the word 'cancer' is 'a serious disease', but in this context of terrorism this word is used indirectly to refer to 'something harmful that affects a lot of people and is difficult to stop'. The incongruity between the basic meaning of disease and the contextual meaning of something harmful is solved when comparing the concept of disease with the concept it indirectly refers to.
In direct metaphors, there is no contrast between the contextual and the basic meaning of the words used: the words introduce a new referent in the text that is incongruous with the context. Direct metaphors are often part of an explicit comparison or simile (Steen and Dorst 2010) and they often occur with some marker or flag. An example is (2), an excerpt from an open letter/advertisement by Dutch prime-minister Mark Rutte. In the excerpt, the words 'the Netherlands', referring to a country, are explicitly compared to with a marker 'as' to 'a little vase', relating to a delicate possession: (2) I see the Netherlands as a little vase, which we are carrying with 17 million ordinary and extraordinary people. 2 (Rutte 2018) So, in such direct metaphors, there is no contrast between basic and contextual meaning of the words, but between the referents in the unit and the topic of the text: 'a little vase' refers to a concept from a different domain than 'the Netherlands' in the remaining text.
A direct metaphor need not be a marked simile (see Goatly 1997: 170). An example of an unmarked direct metaphor is the following fragment from a speech by former US president Truman in which he argues why the US should attack Korea right now:

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(3) […] It must be clear to everyone that the United States cannot-and will notsit idly by and await foreign conquest. The only question is: What is the best time to meet the threat and how is the best way to meet it? The best time to meet the threat is in the beginning. It is easier to put out a fire in the beginning when it is small than after it has become a roaring blaze. (The Pentagon Papers 1981: 588) In the last sentence, a new referent from a distinct domain ('fire') is introduced that is incongruous with the domain of the referents in the first part of the text (the threat of war). The statements about how to deal with fire can be related to the statements the threat of war by mapping the domains.
At the conceptual level, cognitive linguistic approaches generally distinguish between novel and conventional metaphors. Conventional metaphors are commonly used in thought and discourse and do not need active mapping from source to target domain to be understood. Their contextual meaning can be found in usage-based dictionaries, as is the case for 'cancer' in 'ISIL's a cancer' in (1). Novel metaphors, on the other hand, connect two domains in new or creative ways and thus do demand cross-domain mapping from the recipient. Fragment (2) contains an example of a novel metaphor where Dutch prime-minister Mark Rutte compares the Netherlands with a delicate vase that needs to be taken care of.
At the communicative level, metaphors can be distinguished based on their purpose in the interaction. Steen (2008) distinguishes between deliberate and non-deliberate metaphors. 3 Deliberate metaphor is intended to change the perspective on the target domain, for instance to clarify complicated matters or to change someone's opinion. Reijnierse (2017) has developed a method to identify potential deliberate metaphor based on text analysis. Metaphors are potentially deliberate if the source domain is part of the referential meaning of the text in which it occurs (Reijnierse 2017: 27). A marker, novelty of metaphor, and extendedness of metaphors can point at deliberate use. Example (2) contains a potentially deliberate metaphor: Prime Minister Rutte invites the reader to think of the Netherlands as a delicate vase. In non-deliberate metaphor this does not happen: the source domain is not meant to play a part in meaning of the utterance (Steen 2011: 102). An example of metaphor use that is likely to be non-deliberate is 'collapsing' in fragment (1): the domain of buildings is not relevant for the meaning of the utterance and no marker is used to draw the attention of the addressee.
The parameters introduced above enable distinguishing between metaphors on various levels and results in several types of metaphor, from direct, novel, and deliberate metaphor till indirect, conventional, and non-deliberate metaphor, and everything in between. These parameters offer a broad view on metaphor and thus enable a broad perspective on accounts of metaphor in argumentation theoretical literature.

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The Study of Metaphor in Argumentation Theory

The Linguistic Dimension of Metaphor
In the previous Section, three dimensions of metaphor were distinguished. Scholars in the argumentation-theoretical field usually do not explicitly distinguish between the three dimensions of metaphor, but that does not mean that these dimensions cannot be inferred from the approach they take and the examples they analyse. In this Section, it will be determined to what extent these dimensions are taken into account in the argumentation-theoretical literature, so it can be explained why an argumentative function is ascribed to some metaphors and not to others. This Section first discusses the linguistic dimension, then the conceptual dimension, and finally the communicative dimension. These categories form the metaphorical parameters in the overview of functions of metaphor in Table 1.
Since argumentation theory concentrates on argumentation in discourse, the linguistic dimension of metaphor generally is the point of departure. Consequently, some authors view metaphors merely as a "special presentational device" (Garssen 2009: 134), that does not add any relevant content to discourse: they would be just a matter of indirect language use (see Sect Specifically in classical rhetorical handbooks, for instance in Aristotle's On Rhetoric (1926), the linguistic dimension of metaphors is the main focus, as metaphors are discussed as part of lexis, the style of a speech. The most influential part of Aristotle's approach is his conception of metaphor as an analogy between different terms. This approach was also taken up by Perelman and Olbrechts-Tyteca (1969: 372) in their approach to analogy as a 'resemblance of structures': concrete term C is to D (the phoros of an analogy) as abstract term A is to B (the theme). The structures can be more complex, when consisting of 3, 6 or more terms. The example in both books is the following: "For as the eyes of the bats are to the blaze of the day, so is the reason in our soul to the things which are by nature most evident of all" (Perelman and Olbrechts-Tyteca 1969: 373). Aristotle considers similes to be metaphorical too. These draw on an explicit, flagged, comparison (e.g. 'as a lion'), while 'regular' metaphors do not (e.g. 'a lion, he Perelman and Olbrechts-Tyteca (1969) consider verbal analogy (in their case, figurative analogy) to be some kind of metaphor, too. Such metaphors can be classified as direct metaphors. They introduce the following example of a verbal

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The Study of Metaphor in Argumentation Theory The Study of Metaphor in Argumentation Theory analogy (which is used argumentatively), in which someone chasing their desires is compared to a child reaching for nuts in a jar: (4) If a child puts his hand into a narrow-necked jar to pull out figs and nuts and fill his hand, what will happen to him? He will not be able to pull it out, and he will cry. "Let a few go" someone will tell him, "and you will get your hand out." So I say to you, do the same with your desires. Wish only for a small number of things, and you will obtain them. (Epictetus, Discourses (Arrian's), bk III, chap 9: 381, in Perelman and Olbrechts-Tyteca 1969: 402). Perelman and Olbrechts-Tyteca (1969) argue that analogies are more persuasive if they are 'condensed' and some kind of fusion of terms takes place, i.e., when terms referring to the source domain are introduced that are incongruous with the target domain referred to in the clause. Such condensed analogies are cases of indirect metaphor, such as 'an ocean of false learning', and 'a hollow account' (p. 402).
Other indirect metaphors contain A is B constructions, such as 'life is a dream' and 'man is a reed' (p. 402).
In other approaches, direct and indirect metaphors are generally not contrasted. Examples of metaphors that can be considered as indirect ones can be found, among others, in Kauffman and Parson (1991), 4 Pielenz (1993), McQuarrie and Mick (1996), and van Eemeren and Houtlosser (2000). Van Eemeren and Houtlosser (2000), for instance, discuss metaphors which can be considered indirect ones in a speech by Senator Edward ("Teddy") Kennedy, such as the metaphorically used 'home' in the sentence "[…] all of us tried to help her feel that she still had a home with the Kennedy family" (2000: 155). Van Eemeren and Houtlosser consider this metaphor use a matter of word choice which evokes associations that support Kennedy's stance.
Examples with direct metaphors generally receive more attention than indirect ones in modern argumentation-theoretical approaches. The following example from Garssen and Kienpointner (2011: 49) stems from an Austrian newspaper editorial that criticizes government policy to place advertisement in a newspaper to gain positive news coverage.
The authors analyse the fragment as a figurative analogy in which the governments behaviour (buying advertisements) is compared with a drug addict needing more and more drugs: (5) The government is misguided with this strategy. Bought cheers never last for a long time. As is the case if you are high, you have to increase the dose in order to achieve the same effect as during the beginning of the addiction. In the end Faymann and Pröll will have lost not only the tax money of all of us, but also their credibility. (Salzburger Nachrichten, 28 Nov, 2009, p. 1) This is in fact an example of a direct metaphor, as the second sentence introduces a new domain (of drug addiction), which is here flagged with 'as is the case', inviting a crossdomain mapping. Other indirect metaphors in this fragment, such as 'cheers' and 'high' are not addressed. These words have a contextual meaning that deviates from the concrete more basic meaning 5 but can be related to the basic meaning through some kind of similarity.
Another often cited example that can be regarded as direct, but unmarked, metaphor was already introduced in example (3), in which Truman argues for a direct US attack on Korea: (3) […] It must be clear to everyone that the United States cannot-and will notsit idly by and await foreign conquest. The only question is: What is the best time to meet the threat and how is the best way to meet it? The best time to meet the threat is in the beginning. It is easier to put out a fire in the beginning when it is small than after it has become a roaring blaze. (The Pentagon Papers 1981: 588) In this fragment, there is an incongruity between the reference to the threat of war and the reference to fire, which can be solved through a cross-domain mapping. Here, again, the same fragment contains not only this direct metaphor, but also several indirect (quite conventional) metaphors, such as 'sit ' and 'meet'. 6 This example was used by Hastings (1962: 114) to illustrate the type of argument he called reasoning from analogy. Hastings did not discuss this example in terms of metaphor. (Garssen 2009) and van Eemeren and Garssen (2014), on the other hand, label this example as a figurative analogy and argue that it is based on a metaphorical relation between two different 'classes of events' (2014: 51-52). The authors mention the classes of fire and war, which are connected through the metaphorical comparison, but they do not use terms as 'direct' or 'indirect' metaphor. More importantly, they ignore the indirect metaphors. Although indirect metaphors are addressed in other publications as stylistic choice (e.g., Eemeren and Houtlosser 2000), they are not taken into account in the argumentative analysis here.
What can be inferred from the cased discussed above is that the distinction between indirect and direct metaphors is not explicitly made in these contributions and their treatment varies. In fact, in many cases, the examples in the literature are not even identified as metaphors and are merely used to illustrate the category of analogy argumentation (e.g., Hastings 1962;Toulmin et al. 1979;Schellens 1985;Govier 1989;Garssen 1997;Walton 2014). Authors may mention that the examples contain references to distinct domains or different classes, but the analogies are not 1 3 The Study of Metaphor in Argumentation Theory necessarily categorized as metaphorical. The linguistic form of a metaphor apparently does influence whether it is seen as a particular argumentative move or not. In these contributions, cases that can be regarded as direct metaphors are considered to be relevant for argument analysis, for instance as analogy argument, while indirect metaphors are not identified or are seen as a matter of stylistic presentation.

The Conceptual Dimension of Metaphor
Although the linguistic level of metaphor has received most attention in argumentation-theoretical literature, more recent studies incorporate cognitive linguistic insights into their approach and take the conceptual dimension of metaphor into account (e.g., Pielenz 1993;Santibáñez 2010;Oswald and Rihs 2014;Xu and Wu 2014). In these contributions, it is argued that certain linguistic expressions in discourse are based on implicit, underlying conceptual metaphors that install a set of correspondences between the source domain and the target domain. These metaphors can constitute a more novel mapping (e.g., the Netherlands is a little vase) or a more conventional one (e.g., time is money). This distinction is a relevant one for argumentation analysis, because novel metaphors require a comparison to be understood (and accepted), whereas conventional ones do not necessarily: through frequent use, conventional metaphors have (gradually) gained the metaphorical meaning as a basic meaning, next to their metaphorical meaning. 7 An example of how conventional conceptual metaphor may work can be found in Pielenz (1993), who analyses an example taken from the book Men on rape (1982), a series of interviews with rapists by Tim Beneke. Pielenz intends to show that conceptual metaphors represent cultural values and attitudes, which end up in our language use, often without us noticing it. To illustrate this, Pielenz cites from an interview with a librarian who justifies his claim that "a woman makes me want to rape her", by arguing that "she's giving off very feminine, sexy vibes". According to Pielenz, such justification is based on multiple related conceptual metaphors, such as 'Sexuality is a violent natural force ' (1993: 153), which imply that the rapist was 'forced' by the woman to rape her. These conventional metaphors are expressed through various indirect metaphors, such as "They have power over me just by their presence" and "they can come up to me and just melt me". So, indirectly, these expressions refer to conventional conceptual metaphors underlying the arguments.
At the linguistic level, conventional metaphors may also be expressed through a metaphorical comparison, but their conventionality may make them more suitable for other uses in discourse. They may for instance function as presuppositions in argumentative discussions, such as NATION is FAMILY in political discourse (e.g., Pielenz 1993;Santibáñez 2010). Such conceptual metaphors may function as implicit assumptions underlying the premises of an argument, and are simply taken for granted by discussants. An analyst may reconstruct such assumptions as fundamental premises for argument (cf. Kauffman and Parson 1991;Xu and Wu 2014), 8 which may constitute starting points for the discussion (see Sect. 4.2).
Novel metaphors do not work in this way: a comparison between domains is required and the assumed mapping between the two cannot be taken for granted. This means that their use differs. A novel metaphor like "The Netherlands is like a little vase" is controversial and is therefore not a likely candidate for introducing common starting points in a discussion.

The Communicative Dimension of Metaphor
On the communicative dimension of metaphor, deliberate and non-deliberate metaphor use is distinguished. Non-deliberate metaphors are used without the intention of drawing particular attention to the source domain. Many of the indirect, conventional metaphors, which are employed because such metaphoric expressions are just the way to talk about the target domain, belong to this category. The cases discussed in both Kauffman and Parson (1991) and Pielenz (1993) involve such non-deliberate metaphors (e.g. 'vibes', 'melt'). Once metaphors are used to direct the attention of the audience to the source domain evoked by the metaphoric expression, they are potentially deliberate. The source domain is then part of the referential meaning of the text (Reijnierse 2017: 27). Deliberate metaphors can be used for various communicative purposes, such as explanation (e.g., Thibodeau et al. 2017), and persuasion or argumentation (e.g. Sopory and Dillard 2002).
Conventional and indirect metaphors can, however, be used deliberately too, if they somehow alert the addressee to see the target domain from the perspective of some source domain. This can be done by a simile, as in direct metaphor, but also by a change in register or by extending a metaphor. Perelman and Olbrechts-Tyteca (1969: 405), for instance, argue that conventional or 'dormant' metaphors can have great persuasive power once they are reactivated, for instance by extending them. The conventional metaphor 'playing with fire' can for instance be revitalized by replacing 'fire' with 'dynamite'. The noun 'dynamite' can then be identified as a potentially deliberate metaphor (Reijnierse 2017: 89).
From the above overview it becomes clear that an array of argumentation approaches exists with varying attention to metaphor. Metaphors are not always explicitly identified as such in the literature, while they do appear in the examples illustrating types of arguments (e.g., Schellens 1985;Walton 2014). In the following section, the possible argumentative functions of metaphors will be further discussed.

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The Study of Metaphor in Argumentation Theory

Argumentative Functions of Metaphor
As was explained in Sect. 2.1, the current paper focuses on the use of metaphor in three prominent moves in a discussion that are distinguished in the pragma-dialectical theory, namely advancing a standpoint, advancing argumentation, and introducing starting points. In this Section, the use of metaphor in each of these moves will be discussed.
A particular type of analogy argumentation is rebuttal analogy: these use analogy to refute a particular claim. In the following, the uses of metaphor as standpoint (4.2), as starting point (4.3) and as various types of argument (4.4) will each be further discussed. Each of these functions of metaphor is illustrated with examples from the literature. Where certain functions of a particular manifestation of metaphor is not addressed in the literature, new examples taken from public discourse (e.g., political speeches, websites) are added.

Metaphor as Standpoint
According to Wagemans (2016), metaphors can function as (part of) a standpoint, as starting point and as (part of) an argument. 9 He conceptualizes metaphor as an explicit metaphorical comparison (and thus leaves out other types of metaphor). A metaphor as standpoint constitutes a proposition that consists of this metaphorical comparison. The examples he gives are the following metaphors: (6) The organism can be compared to a keyboard.
(7) Our soldiers are lions. (Wagemans 2016: 83) In each of these propositions, (elements from the) source and target domain are linked with a verb ('can be compared' and 'are'). At the linguistic level and the conceptual level they are different: (6) is a direct novel metaphor, while (7) is an indirect conventional metaphor (the contextual meaning 'someone who is powerful, impressive, or brave' is in MacMillan's dictionary). Due to the directness and the novelty of (6), this can be seen as a potentially deliberate metaphor: the source domain of a keyboard is part of the referential meaning of the utterance (see Reijnierse et al. 2018). The concept of 'lions' in (7), on the other hand, does not form part of the referential meaning of the utterance, and is therefore potentially nondeliberate. Similar cases are the words 'sit' and 'meet' in fragment (5): they are used metaphorically at the linguistic and conceptual level, but not at the communicative level.
A metaphorical comparison can also function as part of a standpoint if the accuracy or desirability of a metaphor is the issue under discussion. Wagemans presents the following examples of metaphor as part of a standpoint: (8) The brain is a computer is not an accurate metaphor.
(9) The act of thinking about ourselves as machines should not be carried out. (Wagemans 2016: 84-85) The standpoint in (8) not only expresses the metaphorical comparison but also an evaluation of the metaphor, while (9) contains a proposition of policy. In defending such standpoints, discussants point at the similarities or dissimilarities between the domains compared in the metaphorical comparison. Although these examples refer to metaphors, they all concern negative judgments on metaphors and thus also contain arguments negating correspondences between the two domains compared.
One specific use of metaphor as standpoint can occur in extended metaphor, which is one of the signals that a metaphor is used deliberately (Reijnierse et al. 2018). Oswald and Rihs (2014) address extended metaphor in a case study of a Swiss political pamphlet containing the metaphor 'The USA is an empire' as a standpoint. According to the authors, the pamphlet contains various expressions that refer to mappings between source domain (empire) and target domain (USA), which function as arguments (from example) supporting the acceptability of the proposed metaphor. In this case study, the "accuracy, legitimacy and/or relevance of the metaphorical mapping is the standpoint, while the different instantiations of conceptual mappings for different properties count as arguments in support of said standpoint" (Oswald and Rihs 2014: 146). The novel metaphor clearly entails a proposition to which the writer is committed and which is essential in this piece of argumentative discourse.
Conventional metaphor can also be used as (part of a) standpoint. 10 No such case was found in the literature, but the following fragment contains a real-life example. On the homepage of car manufacturer Volkswagen called Volkswagen for Europe, an employee gives his opinion on the European Union, expressing a direct conventional comparison of the EU as a family (see Musolff 2004): (10) The EU is like a big family. People argue, laugh and cry, but they stick together and talk to each other. (Why we vote for Europe 2019) The next example illustrates how conventional metaphor can be extended. The fragment stems from an essay by English author Michael Mopurgo on The Guardian website, arguing that the British people should reconsider the Brexit, and that the UK should not leave the European Union: (11) After all we are a family going through a divorce.
[…] We need to try to commit to this marriage, to make it work better for us, for our children, and for Europe. (Morpurgo 2019, April 4) Mopurgo uses the conventional metaphor to compare the EU membership with a marriage 11 and thus compares leaving the EU to a divorce. Both sentences in this fragment contain indirect metaphors, using words referring to the domain of marriage, such as 'family' and 'divorce'. The sentence "We need to try to commit to this marriage" represents Mopurgo's standpoint. Several other words in the text outside of this fragment refer to the source domain of marriage, such as "family", "process of divorce", "the breakup", thereby extending the marriage-metaphor. The extensions draw attention to the source domain of marriage, which makes this an example of potentially deliberate metaphor. These examples show that also conventional metaphors can be used to directly or indirectly express a standpoint, while their conventionality would seem to make them unlikely candidates for expressing a controversial point of view. However, in these cases, the metaphor is revitalized through extension and thus offers a fresh perspective on the target domain.

Metaphors as Starting Points
Apart from standpoints, metaphors could also play a role in (material) starting points, 12 which function as a point of departure for a discussion ( van Eemeren and Grootendorst 1992: 93-94). Van Eemeren (2010: 121) argues that discussants can use a metaphor that "is likely to appeal to the audience" to introduce a starting point. Santibáñez (2010) and Xu and Wu (2014) consider some conventional conceptual metaphors as 'backing', or material starting point. In the Toulmin model they use, the backing is the argument supporting the warrant, or connection premise. Santibáñez (2010) and Xu and Wu (2014) analyse a newspaper article in which Chilean president Michelle Bachelet is criticized, by describing her 'flaws' in terms of a traditional house wife. In the news article, critics mention their grounds for judging Bachelet as a bad mother and these lead them to conclude that she is not a good president. According to Santibáñez (2010), the step from grounds to claim is justified by the warrant ('All good mothers have to show authority in the house to be a good mother'), which is supported with the backing or starting point 'PRESIDENTS are MOTHERS'. In contrast, Xu and Wu (2014), who propose an alternative analysis, argue that the metaphor 'NATION is FAMILY' is conceived as a (possible) shared starting point constituting the basis of this argument. These conventional, conceptual metaphors can, however only be inferred from the metaphorical expressions in the discourse. Either way, this means that such conventional metaphors expressed in language provide inferable starting points that need to be taken into account when analysing and evaluating argumentative discourse.
Renardel de Lavalette et al. (2019), on the other hand, discuss explicit starting points in discourse. Using a pragma-dialectical framework, they analyse several ways in which metaphor is used, both directly and indirectly, to introduce starting points in a (political) discussion. For instance, in a British Public Bill Committee debate, Minister Grayling introduces the starting point that the bill and the debate on it are not about the details, but about building a framework for the new benefit system. To introduce this starting point, Grayling uses a novel, direct metaphor comparing the bill with building a bookcase: the bill should be a framework (a bookcase) and should not fill in all the details (the books): (12) […] Clause 1 is, effectively, the defining clause of the first part of the Bill, because it sets out provisions for the universal credit. It, and the following clause, creates the framework for the new benefit. For want of a better way of explaining it, they will create a bookcase on which we can lodge the books of the detail of the future benefit system. Both the metaphor in (12) and in (13) are potentially deliberate: the discussants need the domain of the bookcase to make sense of the utterances about the bill.
Also conventional metaphors can be used deliberately to introduce a starting point. For example, in a debate on Brexit at Loughborough University in 2016, Professor Alistair Blair explicitly said that the EU is like a marriage. This is a direct, conventional metaphor. Blair in fact posits that this statement could function as a starting point for arguments of those in favour and of those against leaving the EU 13 :

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The Study of Metaphor in Argumentation Theory (14) The EU is like a marriage of countries-there'll always be problems with it, which would back up leave arguments, but would also support remain. (Wilson 2016) The next example shows how indirect metaphor can be used to introduce a starting point. It is taken again from ( By formulating a rhetorical question, Hendrick implies that the review panel is like a watchdog without 'teeth', which indirectly pictures the review panel as powerless and ineffective. In the response to Hendrick, the indirect metaphor was in fact taken up as part of an argument: (16) The review panel has teeth. It can quash a decision, and it can ask and require a governing body to reconsider a decision. (2019: 15) In the response, part of the starting point is accepted by using the same metaphor, namely the idea of the review panel as a watchdog. The assumption that it has no teeth, however, is denied and is thus not accepted as starting point.
These above examples show that direct metaphors expressing an entire proposition can be used to explicitly introduce a starting point in a discussion and should thus be taken up in an argumentative analysis of discourse. Indirect metaphors may also express a starting point, but due to their indirectness, they present the starting point as if it is generally accepted.

Metaphor as Argument
Besides as standpoint and starting point, metaphors can also function as (part of) an argument. Wagemans (2016) distinguishes between metaphors in the material and in the bridging or connection premise. Starting from his conceptualization of metaphor, the particular place in the argumentation (i.e., the particular premise) affects the exact type of argument we are dealing with: If the metaphorical comparison constitutes the connection premise, the argument rests on an analogy relation, whereas a metaphorical comparison in the material premise results in another type of argumentation, such as argument from sign. In addition, metaphor can be used in a particular type of analogy argument, namely rebuttal analogies. Each of these cases will be further discussed below.

Metaphor as Figurative Analogy Argument
The function of metaphor as a (figurative) analogy argument is in fact the most common one described in the argumentation literature (e.g., Perelman and Olbrechts-Tyteca 1969: 399). In general, argumentation scholars differentiate between literal comparisons ("straightforward/direct/trivial/same-domain" analogies) and figurative ("a priori/indirect/non-trivial/different-domain") analogies. 14 These types are distinguished on one or both of the following two points. Firstly, contrary to literal analogies, in figurative, or different-domain, analogies, the issues compared are not from the same class (e.g., Schellens 1985;Juthe 2005;Garssen and Kienpointner 2011;Walton 2014). For instance, a coalition is compared with a marriage, nuclear waste with oatmeal or nuclear weapons with rain coats (Schellens 1985: 200). Secondly, in literal analogy the issues are similar on the basis of shared characteristics, while in figurative analogy the issues are similar on the basis of abstract principles: the structure of the abstract relationships of the two events is the same (Hastings 1962: 93;Juthe 2005). Figurative analogies therefore require a different analysis and evaluation than literal ones. Critical questions pertaining to the literal analogy scheme for instance ask for sufficient similarities between the entities compared (e.g., Walton 2014), and are therefore not directly applicable to figurative analogies.
Not every figurative analogy, however, is necessarily argumentative. As Schellens (1985: 200) argues, the analogy is argumentative if it is connected to a particular claim in a context of disagreement. The following figurative analogy, for instance, is simply an (explanatory) statement: (17) The circulatory system is to the body as the free exchange of information is to a democracy. (my transl.) (Schellens 1985: 200) The statement in (17) could still function as argumentative in a context in which it is connected to a conclusion such as 'A democracy in which the press is restricted, is destroying itself'.
In argument from figurative analogy, the connection premise contains a metaphorical comparison. Using Toulmin's (1958) terminology, Musolff (2004: 60) also recognizes the function of metaphor in the connection premise. He argues that "in metaphorical arguments […] the warrant is analogical". The warrant in Toulmin's terminology can be understood as the connection premise in pragma-dialectics: it represents the premise that guarantees the transference of acceptability from data (i.e., the material premise) to claim (i.e., the standpoint) (Gerritsen 2001: 60). Musolff (2004: 34) does not completely apply Toulmin's model of argument, but argues that a metaphorical statement like "We must join the European train as quickly as possible" leads to political conclusions based on the underlying analogy: (18) Just as it is (normally) preferable to catch a real train (A) in time and therefore enter it quickly when it is about to leave (B), so the political process that is considered to be the European train leaving for the destination of currency union (C) should be joined as soon as possible (D). (Musolff 2004: 34) 1 3

The Study of Metaphor in Argumentation Theory
The following real-life example illustrates the role of (in this case, direct) metaphor in figurative analogy. It is a fragment from the personal website of John Redwood, a UK conservative MP, who often provides political commentaries in the media: (19) Being in the EU is a bit like being a student in a college. All the time you belong to the college you have to pay fees. You have to obey all the rules of the institution. When you depart you have no further financial obligations. (Redwood 2017) In this fragment, Redwood argues that the UK does not have any financial obligations when leaving the European Union, because a student does not have such obligations when leaving college, and being an EU member is like being a college student. The analogy contains an explicit metaphorical comparison in the connection premise. The argumentation can be reconstructed in the following way 15 : (1.) (When the UK leaves the EU, they have no financial obligations.) 1.1a All the time you belong to the college you have to pay fees. You have to obey all the rules of the institution.
1.1b When you depart college you have no further financial obligations. 1.1a/b' Being in the EU is a bit like being a student in a college. The structure visualizes the function of the metaphorical comparison as the connection premise (1.1a/b'), connecting the source domain of being in college with the target domain of being an EU member. The connection premise supports the justificatory force of the argument: it enables transferring the acceptability from the argument to the standpoint by using the principle of analogy. It is important to note that although the metaphorical comparison functions as the connection premise in the discourse, the material premises in fact also contain metaphor-related words: they are direct metaphors referring to the source domain of the metaphor ('All the time you belong to the college you have to pay fees').
The connection premise can also be expressed through an indirect metaphor in an 'A is B' construction as in the following remarks by Donald Tusk, former president of the European Council, in which he talked about European nations' solidarity with Ireland during the negotiations with the UK about Brexit: (20) The European Union is a family of free nations, linked by values. For sure, we may not always be in agreement on everything. But in times of trouble, families come together and stand with each other. For the EU27, this is especially true when we talk about Brexit. (Remarks by President Donald Tusk after his meeting with Taoiseach Leo Varadkar. 8 March 2018. https ://www. consi lium.europ a.eu/en/press /press -relea ses/2018/03/08/remar ks-by-presi dentdonal d-tusk-after -his-meeti ng-with-an-taois each-leo-varad kar/) In this fragment, Tusk draws a conventional cross-domain mapping between family and the EU which functions as a connection premise: he states that families come together in difficult times and that therefore, EU nations will stand together, too. This argument thus rests on an analogy between family and the EU.
The connection premise of an analogy argument can be made explicit (as in (15) and (16)), but is also often left implicit. Wagemans (2016) illustrates the use of metaphor as the implicit connection premise with the analysis of a speech fragment by former U.S. president Abraham Lincoln in 1864. In this fragment, Lincoln supposedly argued why he should not be replaced during the civil war: (21) I have not permitted myself, gentlemen, to conclude that I am the best man in the country; but I am reminded, in this connection, of a story of an old Dutch farmer who remarked to a companion once that "it was not best to swap horses while crossing a stream". (Wagemans 2016: 89) Wagemans reconstructs the example as follows: (22) Standpoint: The act of replacing a president in the middle of a war should not be carried out. Material premise: Because: The act of swapping horses while crossing a stream should not be carried out. Bridging premise: Replacing a president in the middle of a war can be compared to swapping horses while crossing a stream. (2016: 89) In this example, a direct, potentially deliberate metaphor is used in the material premise which evokes the metaphorical comparison that functions as the (implicit) connection premise.
Some authors are hesitant in classifying metaphor in argumentation as figurative analogy (cf. Juthe 2016: 19-20). Two main reasons are that metaphors would not rest on (sufficient) similarities and that figurative analogies would not be genuine arguments (cf. Garssen 2009). The question whether metaphor rests on similarity or not is also debated in cognitive linguistic studies (e.g., Lakoff and Johnson 1999). Steen (2007: 61-63) argues that metaphor can be defined by similarity, if understood to include literal and relational similarity. So analogous cases do not (necessarily) share similar attributes, but share analogous relations between the elements of the case (Juthe 2005(Juthe , 2016Xu and Wu 2014).
A reason for not considering figurative analogies as 'real' and possibly reasonable arguments and instead as merely a presentational device, is that the two situations compared would only share one characteristic, while in normal comparison argumentation there would be multiple similarities (Garssen 2009). However, as was argued above, there need not be a series of shared characteristics to speak of (reasonable) analogy argumentation, because the analogy rests on a similarity in the abstract structure of the two elements or events compared (e.g., Hastings 1962;Schellens 1985;Govier 1992;Juthe 2005). 16 As such, critical questions can still 1 3 The Study of Metaphor in Argumentation Theory apply and can still distinguish reasonable from unreasonable figurative analogies (cf. Garssen and Kienpointner 2011;Govier 1992: 165-166).
This Section has shown examples of both direct and indirect metaphors functioning in figurative analogies in argumentative discourse. They may be unreasonable if they do not stand the critical test, but they should not be discarded as arguments all together just because they may be weak. Yet, even if metaphors and analogies may be used argumentatively, this does not mean that they should all be considered as argumentative as they could also function as illustration (cf. Schellens 1985: 200). Moreover, not all metaphors in arguments constitute analogy arguments.

Metaphors as Other Types of Argument
A metaphorical comparison may function as the connection premise in an analogy argument, but may also function as a material premise in some other type of argument, such as argument from sign (Wagemans 2016). The following is a constructed example from Wagemans is inspired by the commonly used 'the brain is a computer' metaphor (see Finsen et al. 2019) and has a metaphorical comparison as the material premise: (23) Standpoint: Human beings are not responsible for their actions. Material premise: because human beings are machines. Bridging premise: Being a machine is a sign of not being responsible for your actions. (Wagemans 2016: 88) In this example, the standpoint is supported with symptomatic argumentation, or argument from sign. The fact that human beings belong to the class of machines is used to conclude that human beings also have the characteristic that belongs to machines. 17 The direct metaphor in example (2) in fact has the same function: Prime Minister Rutte argued that he sees the Netherlands as a little vase to justify his standpoint that the people should treat the Netherlands carefully, and delicate vases need to be cared for. So depending on whether the metaphorical comparison is used in a connection premise or a material premise, it functions as an analogy argument or a different kind of argument (e.g., symptomatic), respectively.
As was argued in Sect. 4.2, metaphorical comparisons can also function as (sub) standpoint and can then also be further supported with subordinate (symptomatic) arguments (see, e.g., Oswald and Rihs 2014). In the example of Chilean president Bachelet mentioned earlier, Santibáñez (2010) and Xu and Wu (2014) analyse how metaphorical expressions are used in support of a figurative analogy argument. In the article, Bachelet is described in terms of a (traditional) mother who does not fulfil her duties, e.g., 'the lady of the house does not give orders, does not know what to say'. These metaphorical statements are used as material premises to argue that Bachelet is not a good mother, which, based on the metaphor PRESIDENTS are MOTHERS/NATION is FAMILY, allows the critics to conclude that Bachelet is not a good president. The metaphorical expressions are here used in symptomatic arguments pointing at characteristics of a bad mother.
Apart from these direct metaphors constituting entire premises in argumentation, all types of arguments can contain indirect metaphors as part of their premises. An example of an indirect but deliberately used metaphor is the following from Renardel de Lavalette, Andone and Steen (2019). The example stems from the British debate segment in which Minister Grayling compares a welfare bill with building a bookcase. Opposition member Gilmore argues why they are right in asking about the details of the bill nonetheless: (24) That will be important for us, because otherwise we will be buying that empty bookcase, which is a difficult thing to sell to people. (Renardel de Lavalette et al. 2019: 11) Here, Gilmore's partly implicit argument is that: 'if the opposition would not ask about the details, they would be buying an empty bookcase (which is undesirable)'. The argument containing the deliberately used metaphor 'bookcase' to refer to the framework for the bill is in fact a pragmatic argument, pointing at the negative consequences of not doing what was mentioned in the standpoint. 18 The indirect metaphor is part of the material premise of a pragmatic argument here. So, direct metaphorical comparisons can constitute entire premises, either as connection premise in an analogy argument or as a material premise in symptomatic argument. Indirect metaphors with 'A is B' construction can work in similar ways. Indirect metaphors without this construction can merely be used as part of a premise; yet, they are not restricted to a type of premise or type of argument.

Metaphors as Rebuttal Analogies
All types of arguments can in fact also be used as counterargumentation, which is to attack the opponent's claim. A specific type of refutational argument in which metaphor is likely to occur is the rebuttal analogy. A rebuttal analogy refers to an absurd action or line of reasoning in the source domain and maps this onto the action or reasoning in the target domain. The speaker reacts to a proposition P1 and argues that 'P1 is like P2' and that P2 is absurd, thus rendering P1 absurd, too (Colston 2000: 338). 19 In a report on a road test of Alfa Romeo's new Stelvio, British television host Jeremy Clarkson uses the following rebuttal analogy to demonstrate the absurdity of Alfa Romeo's decision to produce this car:

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The Study of Metaphor in Argumentation Theory (25) I was thinking: "What in the name of all that's holy was Alfa Romeo thinking of?" If you have a heritage as glamorous and as achingly cool as Alfa's, why would you want to make a bloody school-run car? That is like Armani deciding to make carrier bags. (Clarkson 2017) In the last sentence, 'that' refers to Alfa making a school-run car, so this last sentence contains a direct metaphorical comparison between Alfa making school-run cars and Armani making carrier bags. The metaphor is flagged with the words 'that is like'. The comparison here functions as the connection premise, while the material premise contains a reference to the source domain of Armani making carrier bags: (1) (It is absurd that Alfa made a school-run car) (1.1) (It would also be absurd if Armani would make carrier bags.) 1.1' [Alfa making school-run cars] is like Armani deciding to make carrier bags.
Although this type of move has the particular function of refuting a claim, it works in a similar way as regular figurative analogy argumentation. The connection premise namely consists of a metaphorical comparison between source and target domain. Since part of the persuasive power of the rebuttal analogy lies in the absurdity of the novel comparison, the connection premise with the metaphorical comparison is best made explicit and marked ("That is like Armani deciding to make carrier bags").

Overview of Functions and Dimensions of Metaphor
The previous Sections reviewed to which extent the three different dimensions of metaphor play a role in argumentative approaches and which argumentative functions can be ascribed to metaphor. The distinct types of metaphors and the different possible argumentative functions are integrated in Table 1. The table provides  For instance, the deliberate use of direct conventional metaphor seemed to be overlooked. The examples in the current study demonstrate the potential of such metaphors in argumentative context. In the literature, more attention was paid to examples containing novel direct metaphors, such as (3) ('It is easier to put out a fire in the beginning when it is small than after it has become a roaring blaze'). These seem particularly suitable for analogy arguments. The 3-dimensional approach to metaphor provides good explanation for the attention to such metaphor: novel, direct metaphor is most likely to be used deliberately. This makes particular sense in an argumentative context in which one intends to convince an audience of a controversial position.
Argumentative discourse in fact also contains indirect conventional metaphors. These are, however used non-deliberately, unless the underlying metaphor is extended or revitalized. This happens for instance when a discussion party first introduces a direct cross-domain comparison which is then extended in the discussion later on.
Certain cells in the table are left blank because not all of the options that are distinguishable are really possible or likely to occur in actual discourse. For instance, a novel direct metaphor cannot be non-deliberate as novelty and directness explicitly draw attention to a new perspective on the target domain. The cells for conventional metaphor in the row of rebuttal analogy are empty, too. Such analogies thrive on an absurd comparison that surprises the audience and thus only make sense if a novel metaphor is used. Direct metaphors do not appear as part of an argument or standpoint in the table either. This is due to the fact that direct metaphor represents an entire premise and thus functions as an argument, standpoint or starting point on its own.
The pragma-dialectical perspective adopted in this study lays bare the potential of metaphor in different discussion moves. Apart from the commonly discussed analogy argumentation, this perspective also shows the function of metaphor in for instance starting points.

Conclusion and Discussion
The attention to metaphor in argumentation theory has predominantly been limited to its rhetorical or stylistic role and has not taken into account the various dimensions of metaphor. A review of the argumentation-theoretical literature dealing with (verbal) metaphor shows that only a few studies grant some argumentative function to metaphor and that many studies have a restricted view on metaphor (if addressed at all), as an analogy in language. The current paper set out to use the pragma-dialectical theory, which distinguishes different discussion moves, and the 3-dimensional model of metaphor (Steen 2008(Steen , 2017, which differentiates between the linguistic, conceptual and communicative dimension of metaphor, to offer a more comprehensive approach to the functions of metaphor in argumentative discourse. Based on these methodologies, we can distinguish standpoints, different types of arguments and starting points on the one hand, and direct and indirect, novel and conventional, and deliberate and non-deliberate metaphor on the other hand. Based on these variables, I have compared the ways in which argumentation scholars take metaphor into account.
This review shows that the argumentation-theoretical literature is ambiguous on the argumentative potential of metaphor. There are several explanations for this ambiguity.
First, metaphors are not always explicitly identified as such in the literature, while they do appear in the examples illustrating types of arguments (e.g., Schellens 1985;Walton 2014). This may imply that the authors of these contributions do not ascribe any specific argumentative function to those metaphors or that they just did not take this aspect of argumentative discourse into account. Still, these metaphors may have an argumentative (or another communicative) function.
Second, the explicit references to the function of metaphor also paint a diverse picture: some authors explicitly ascribe an argumentative function to metaphor (e.g., Musolff 2004;Perelman and Olbrechts-Tyteca 1969;Santibáñez 2010;Wagemans 2016), while others deny or ignore such possibility (e.g., Toulmin et al. 1979;Garssen 2009). It should be noted though that what the term 'argumentative' means exactly is up for discussion as well. For instance, some authors argue that metaphor does not have an argumentative function, but can have a rhetorical or persuasive function (e.g. Garssen 2009; Plug and Snoeck Henkemans 2008)-which are qualifications that partly overlap.
Third, contributions discussing metaphor do not depart from the same conception of metaphor and do not distinguish between deliberate and non-deliberate metaphor. When one only considers indirect metaphor, while another only considers explicit metaphorical comparisons to be metaphor, different conclusions regarding the potential of metaphor are drawn: the use of the indirect metaphor 'home', for instance, is taken up as presentational means to enhance persuasiveness (Sect. 3.1), while the direct metaphor in example (5) comparing the government buying advertisements is compared with a drug addict is conceived of as a complete analogy argument.
Based on the variables taken from the 3D model of metaphor and the pragmadialectical theory, we can conclude that metaphors may have various functions in argumentative discourse, represented in Table 1. The current study reveals that not all possible functions of metaphor have been taken into account. The role of conventional direct metaphors, for instance, has been largely neglected. The current study also shows that in conventional indirect metaphors may occur in many argumentative moves, but without having a particular argumentative function. If an indirect metaphor is preceded with a direct conventional metaphor, it can constitute an argumentative move, such as the introduction of a standpoint, starting point or connection premise.
In the literature, novel metaphor received most attention, in particular as part of an analogy argument. In such cases, the metaphor is presented directly, thereby inviting the cross-domain mapping on which the argument is based. The review shows, however, that indirect novel metaphors may also have a function as a starting point or as an argument. Again, this occurs most likely after the novel cross-domain mapping was introduced directly.
Table 1 also shows that certain cells remain blank, because the combination of variables is impossible of unlikely to occur. A novel direct metaphor, for instance, is by definition deliberate as novelty and directness explicitly invite a cross-domain mapping. A rebuttal analogy requires a novel metaphor because it depends on the absurdity of a comparison. In addition, direct metaphors do not appear as part of an argument or standpoint in the table, because they represent an entire premise and thus functions as an argument, standpoint or starting point on their own.
The outcome of this study also affects the analysis of metaphor in argumentative discourse. For instance, the analyst needs to be aware of the linguistic manifestation of metaphor (direct/indirect) to determine whether a metaphor is relevant for the reconstruction of the argumentative discourse. When a metaphor is direct, it involves a separate reference to the source domain, so it adds relevant content to the discourse that somehow needs to be taken into account in the analysis. As a consequence, the analysis cannot do away with such metaphor use as being merely a means of presentation which can be simply rephrased. Such metaphors do not necessarily represent analogy argumentation, but they could. Indirect, conventional metaphors are most likely to be non-deliberate and thus may be analysed as merely 'presentational device' which may be rephrased. Such metaphors may also be part of a premise, without any restriction to the type of premise.
What would this mean for the example (1) in the Introduction? We can conclude that the indirect conventional metaphor 'ISIL's a cancer that's threatening to spread' forms the basis of Carter's argument. It can be interpreted as a deliberately used metaphor, because it is extended and in the second sentence it is presented directly with the flag 'like', thus including the source domain of cancer in the referential meaning ("Like all cancers, you can't cure the disease just by cutting out the tumor"). Based on how one would treat a spreading cancer, Carter defends his strategy of treating ISIS. The 'ISIL's a cancer that's threatening to spread' thus functions as the connection premise in an analogy argument. The third sentence represents Carter's standpoint: 'You have to eliminate ISIS wherever is has spread'. This example shows that taking into account the dimensions of metaphor, help determining its argumentative function.
The overview of types of metaphor and their possible argumentative function enables a more systematic, complete and precise study of metaphor in argumentative discourse. It lays bare the potential of metaphor to be further explored in descriptive, analytical, and experimental research.
The current study could be further elaborated by considering types of discussion moves that were not taken into account here, As explained in Sect. 2, there are more argumentative moves distinguished in the pragma-dialectical theory than addressed in this study, such as casting doubt, requesting and providing explications, and establishing the result of the discussion (see van Eemeren and Grootendorst 1984: 98-105). Insights into the frequency of metaphor in different genres could be enriched by corpus studies taking into account the frequency of metaphor in particular moves in argumentative genres (cf. Reijnierse et al. 2019).
Another area for further research is the rhetorical function of metaphor. Metaphors can be considered as a particular mode of strategic manoeuvring as they involve an opportune selection from the topical potential (by relating the subject of discussion to a particular domain), a particular form of presentation (by using the words associated with this other domain), and an adaptation to the intended audience (by directing attention to a domain of particular interest of the audience) (See van Eemeren and Houtlosser 2000). Metaphor can, for instance, be used strategically to introduce complex issues in more accessible and effective ways and to avoid commitment to certain associations that are evoked by connecting the source domain to the target domain (Feteris 2012).
The relation between the argumentative functions of (extended) metaphor and framing is another fruitful avenue for further research that could not be addressed here. The examples in this study show that certain indirect metaphors function as particular argumentative moves once a cross-domain comparison is first established by a direct metaphor which is then extended. This may be viewed as a frame that enables the interpretation of consecutive moves (cf. Reijnierse et al. 2015;Thibodeau 2017). Studies on the effectiveness of metaphors could also benefit from the current research, as persuasiveness could be linked to their particular dimension and argumentative function. It would, for instance, be interesting to further investigate the effect of particular properties of metaphor in relation to particular discussion moves, such as the role of novelty of metaphor in different types of arguments (cf. Sopory and Dillard 2002). Also, the relation between such properties and the (perceived) reasonableness of discussion moves could be examined (cf. Ervas et al. 2018).
This review has shown that metaphor is a multidimensional phenomenon that may be relevant in argumentative discourse not only as creative presentation but also as (part of) various relevant argumentative moves in a discussion. Being aware of the dimensions of metaphor ánd of its potential in argumentation would therefore enrich argumentation studies and metaphor studies alike.