Historical background: inductive metaphysics in 19th century and early 20th century philosophy
Erich Becher (1882–1929) can be placed in the tradition of inductive metaphysics, a tradition that emerged in the mid- and late nineteenth century and the early twentieth century in Germany.Footnote 6 Besides Becher himself, representatives of inductive metaphysics include Gustav Theodor Fechner (1801–1887), Rudolph Hermann Lotze (1817–1881), Wilhelm Wundt (1832–1920), Oswald Külpe (1862–1915) and Eduard von Hartmann (1842–1906). One way of telling the story of the beginning of inductive metaphysics in mid-nineteenth century is to describe it as a counter-reaction to German Idealism,Footnote 7 which consisted in particular in redefining the relationship of metaphysics to the natural sciences. The idealist Naturphilosophie – especially Hegel’s, the dominating Naturphilosophie at that time – came to be seen as a failure, especially in the eyes of the natural scientists of the time (e.g. Schleiden, 1844; Helmholtz, 1862, p. 164; cf. Külpe, 1904 , p. 6; Schnädelbach, 1984, p. 77). The advocates of inductive metaphysics primarily held the dialectical method of the idealists responsible for this.Footnote 8 They proposed a different method for metaphysics. Their program is based on the idea of remodeling metaphysics according to the empirical sciences; in particular, they propose to use empirical sources and inductive forms of inference in metaphysics, just as empirical sciences have been doing for a long time.
Becher situates himself into this tradition of inductive metaphysics, and just like other proponents of inductive metaphysics before him,Footnote 9 Becher looks out for deeper connections between metaphysics and the natural sciences, with the goal of remodeling metaphysics according to the natural sciences. Let us take a closer look at his particular way of unfolding this program.
Metaphysics and the natural sciences
Becher develops his version of inductive metaphysic in several writings. A good starting point is his small book Metaphysik und Naturwissenschaften (1926b), which has the goal to synoptically summarize his position concerning the relationship between metaphysics and the natural sciences. I will use this book as the basis for presenting Becher’s position, but will use other writings—in particular, his more detailed presentations Naturphilosophie (1914) and Geisteswissenschaften und Naturwissenschaften (1921) – in some places to deepen the understanding of Becher’s position.Footnote 10
Becher begins his investigation of the relationship between metaphysics and the natural sciences with a systematic comparison between them.Footnote 11 According to his approach, sciences can essentially be characterized and distinguished by three aspects: (1) their objects, (2) their methods, and (3) their ultimate basis of knowledge (Becher, 1926b, p. 3). Let us take a look at these three aspects in turn.
The objects of the natural sciences and the object of metaphysics
As the objects of knowledge of the natural sciences, Becher identifies the natural objects, which he regards as real physical objects,Footnote 12 and their properties, their relationships and the processes in which they are involved (Becher, 1926b, p. 4). But individual natural sciences always deal only with certain parts or aspects of the physical world: botany, for example, studies other parts of nature than geology; and even physics, which seems to affect all areas of nature, only examines certain aspects of natural objects, and these aspects are different from those examined by chemistry, for example (Becher, 1926b, p. 5). Accordingly, Becher calls the natural sciences partial real sciences [Partialrealwissenschaften].
Metaphysics, on the other hand, takes an all-encompassing perspective on the world. As the object of metaphysics Becher determines the total reality [das Ge-samtwirkliche]. Accordingly, metaphysics is the science of the total reality, or total real science [Totalrealwissenschaft] (Becher, 1921, p. 323; 1926b, p. 5).Footnote 13 This perspective opens the view to more fundamental questions than those considered in the individual sciences, for example, the questions of the emergence and the meaning of the overall reality (Becher, 1921, p. 319; 1926b, p. 6).
Metaphysics, too, sometimes considers certain parts or aspects of reality, but, unlike the natural sciences, always in relation to the overall reality. Biology, for example, is concerned with organic life, while metaphysics deals with the question of how organic life is related to other parts of the overall reality, e.g., to the soul or consciousness. In this way, it can be said that metaphysics and the natural sciences touch or even overlap each other with regard to their objects. However, through its perspective on the overall reality, metaphysics makes a claim that goes beyond a mere juxtaposition of the results of the individual sciences (Becher, 1921, p. 319).Footnote 14 But, as Becher (1926b, p. 7) emphasizes, these overlaps mean that metaphysics can base its investigations on the results of the individual sciences, which is of course entirely in line with the idea of inductive metaphysics.
The basis of knowledge and the method of the natural sciences
After this determination of the relationship between the natural sciences and metaphysics with respect to their objects, the next question that arises is how they relate to each other in terms of their basis of knowledge and their methods. Becher discusses these two points together and first focuses on the natural sciences. As we will see in Sect. 2.2.4, according to Becher the method of metaphysics can be derived directly from the analysis of the method of the natural sciences.
As he points out, the natural sciences are characterized by a particular method, namely the empirical-inductive method (Becher, 1926b, p. 16), which he analyses in detail. Within this method, the natural sciences take their starting point from perceptions, as their ultimate basis of knowledge. The reason for this, according to Becher, is simply that the process of perception is the only way we can directly grasp what is real (Becher, 1921, p. 116). Strictly speaking, he holds that we only have direct access to our own present consciousness content. But he points out that we can transcend the realm of our present consciousness by using certain principles of cognition, which play an important role in the empirical-inductive method of the natural sciences, as well as in everyday life.
He names three such principles as being most important for the natural sciences (Becher, 1926b, p. 17): the presumption of the trust in memory [Voraussetzung des Erinnerungvertrauens], the presumption of lawfulness [Gesetzmäßigkeitsvoraussetzung], and the causal principle [Kausalprinzip].Footnote 15 The presumption of the trust in memory is a basic principle which we also rely on in everyday life. The presumption of lawfulness and the causal principle, on the other hand, are based on a more fundamental presumption, the presumption of regularity [Regelmäßigkeitsvoraussetzung] (Becher, 1921, p. 231). As Becher points out, the weaker presumption of regularity is in play in our pre-scientific, everyday perception of reality. The stronger presumption of lawfulness and the causal principle are strengthened versions of the presumption of regularity and they are a product of science, in particular of natural science. We will confine ourselves to a closer look at the two basic presumptions, the presumption of trust in memory and the presumption of regularity.Footnote 16
According to the presumption of the trust in memory, we presume that our memory of the past is at least in principle reliable. Memories are present contents of consciousness, which we understand as reproductions of past experiences (Becher, 1914, p. 80; 1921, p. 223). In the absence of counter-reasons,Footnote 17 we usually trust these representations. But as Becher points out, it is not possible to rule out the possibility that our memory always deceives us—there is no way to prove the reliability of memory a priori. Furthermore, the reliability of memory cannot be empirically justified, either: we cannot empirically test the reliability of our memories without making recourse to the past. In order to do so, we would therefore have to presuppose the reliability of our memory, so that such an empirical justification of the reliability of memory would always be circular (Becher, 1914, p. 81).
In the absence of any a priori or empirical justification, we have no choice but to generally trust the reliability of our memory without being able to prove or justify it. The reason why we still have to trust the reliability of our memory is that it is a presumption that is necessary for the attainment of knowledge [erkenntnisnotwendig]. Without it, we could not transcend the realm of our present consciousness; in particular, we could not gain any knowledge of the past. That is, we rely on it because it is indispensable for our cognitive purposes (Becher, 1914, p. 81; 1921, p. 224).
But without the inclusion of further principles, our knowledge would still be enclosed in the realm of our present and past consciousness. In order to transcend this realm, we are dependent on another principle, namely the presumption of regularity (Becher, 1914, p. 84; 1921, p. 227). First of all, this principle is a presumption of regularity regarding our own experiences.Footnote 18 If we want to infer from our past experiences something about experiences that we will make in the future, then we rely on the principle that rules which we could observe in the realm of the experiences made so far will also hold true in the future. Without such a presumption, we could never transcend the realm of our present and past consciousness. This is why this presumption too is indispensable for our knowledge [Erkenntnis], both in everyday life and in the sciences. But just as in the case of the presumption of trust in memory, Becher states that the presumption of regularity can neither be justified a priori nor (without circular reasoning) empirically (Becher, 1914, 88 ff.).Footnote 19 It is a principle on which we have to trust if we want to gain knowledge about the future at all. So we cannot say that the principle can be justified in the sense that we can give reasons for its truth. Nevertheless, we are in a certain way justified in applying this principle, because it is the only way to gain empirical knowledge at all (Becher, 1921, p. 228).
As can easily be seen, this principle is very fruitful in that it licenses several forms of inferences. Becher explicitly mentions analogical inferences and inductive generalizations, which, according to him, are closely related forms of inference (Becher, 1914, p. 87). An analogical inference is for example when I first determine that certain states of my consciousness, e.g. pain, are correlated with certain reactions of my body,Footnote 20 e.g. screaming, and then, when I hear another person screaming, I infer by analogy that she also has a corresponding sensation of pain. An inductive generalization is for instance when I infer from the observation that mercury has always expanded when heated, that this will also happen in the future when mercury is heated (or more generally: in all unobserved cases). It is clear that both kinds of inference rely on the presumption of regularity. The last example also makes clear how important the presumption of regularity is for the natural sciences: every inference to a law of nature is based on an inductive generalization and thus on the presumption of regularity (Becher, 1914, p. 88).
Becher also notes that the presumption of regularity allows us to draw inferences to the past. For example, I can infer that I experienced summer and winter as a five-year-old, even if I cannot remember it (Becher, 1921, p. 227). However, this also means that sometimes the results I obtain on the basis of the presumption of trust in memory and those I obtain on the basis of the presumption of regularity can conflict with each other. Then we have to decide which of the knowledge principles involved should be given priority in the present case.Footnote 21 This means that these principles, which are necessary for gaining knowledge, are not presuppositions that are incontestable in every instance. In particular, conflicts with the results of other principles of cognition—or even with other results based on the same principle—can call certain applications into question. In this sense, these principles are not presuppositions we hold on to come what may, but presumption rules with rebuttable presumptionsFootnote 22: we hold them true until there are reasons to the contrary.
Becher’s realism and its empirical-inductive justification
So far, strictly speaking, we have not gone beyond the realm of our own consciousness: The presumption of the trust in memory allows us to infer to past states of our own consciousness; the presumption of regularity allows us to infer from past experiences to future experiences. While this makes it possible to transcend the present contents of consciousness, we have not yet taken a step out into the external world. But as we have seen above, Becher holds that the natural sciences, as well as metaphysics, have real physical objects as their objects of knowledge. In fact, Becher explicitly holds that we can have knowledge of real objects, and that this is a kind of knowledge that is not limited to metaphysics, but also can be found in the natural sciences and to a certain extent also in everyday life. We must therefore ask how it is possible to expand our knowledge of our own present, past and future consciousness in such a way that we can gain knowledge of objects of the external world.
We have already seen above that Becher bases inductive generalizations and analogical inferences on the presumption of regularity. We will now see that in the justification of his realism, he implicitly relies on another form of inductive inference,Footnote 23 namely Inference to the Best Explanation,Footnote 24 without explicitly reflecting on this form. As will become clear, his usage of this inference form in the justification of his realism shows that inferences to the best explanations are based on the presumption of regularity, just like inductive generalizations and analogical inferences. This is particularly interesting because it is an instructive example that shows how central the inference form Inference to the Best Explanation can be for inductive metaphysics.Footnote 25
Becher points out that knowledge of real objects is, like knowledge of the future, based on the presumption of regularity.Footnote 26 According to his reconstruction, we introduce the assumption of the existence of real objects in order to be able to view the overall reality as more regular (Becher, 1914, p. 163). If we assumed that only our own consciousness existed, much of what happened – which would then be limited to our own states of consciousness – would not follow any rules. If I concentrate on the content of my consciousness, a sudden loud noise, for example, is an occurrence that is not related to any previous content of my consciousness according to any rule. If, on the other hand, I expand the context by postulating the existence of external objects, which I can then understand as causes of my perceptual experiences, I can thereby embed my experience of a loud noise into a regular overall context. The loud noise can then be causally explained by an external process that regularly results in loud noises, such as the unloading of wooden planks (Becher, 1914, p. 86). And the same with many more of my experiences. Becher also points out that we do not have to start from scratch to create such a theory about how external objects cause our perceptions. Already our pre-scientific cognition accomplishes a great deal in this respect; the natural sciences have even expanded the picture created by pre-scientific cognition into a very powerful theory (Becher, 1914, p. 175).
I now want to argue that this postulation of external objects is supported by an inference to the best explanation. As I want to show, this is made clear by several passages.
First of all, the method of Inference to the Best ExplanationFootnote 27 starts with a set of observed phenomena that require an explanation. In a second step, various hypotheses are considered which, if they were true, would explain the observed phenomena. These hypotheses are then compared to determine which of them explains the phenomena best. When it is determined which hypothesis offers the best explanation, the inference is drawn: We infer to the hypothesis which is considered to be the best explanation of the observed phenomena (Lipton, 2004 , p. 56; Bartelborth, 1996, p. 141).
As we have just seen, Becher introduces the hypothesis that there are real external objects as a causal explanation for our sequences of perceptions, in order to make the overall world as regular as possible. The explanation is therefore based on the presumption of regularity: against the background of the presumption of regularity, this hypothesis is the best explanation of the (otherwise irregular) sequence of our perceptions.Footnote 28 It is a good explanation exactly because—and to the extent that –, in accordance with the presumption of regularity, it displays the overall world (including our sequences of perceptions) as highly regular.
Let us now take a look at passages in which Becher rules out alternative hypotheses because they cannot (or at least not sufficiently) explain the emergence of our sequences of perceptions.Footnote 29 For example, Becher considers the fictionalist position that the external world is merely a fiction that we use for orientation and as a means to predict future perceptions (Becher, 1914, p. 171). He dismisses it, however, because the advocates of such a position admit that our perceptions appear as if there were external objects—a fact for which this position, in contrast to realism, then offers no satisfying explanation (Becher, 1914, p. 172).Footnote 30
In a similar way he excludes the idealist positions of Kant and Fichte, according to which the understanding or the I constructs the sensual world of appearance. Becher emphasizes that the idealist theories do not offer a good explanation for the fact that children, despite their ignorance of astronomical laws, see the moon in the right place, i.e. exactly in the position in the sky that it must occupy according to the calculations of astronomers (Becher, 1926b, p. 12). The idealists would have to hold that the understanding or the I of children places the appearance of the moon exactly in the right position, and it is not understandable how they should be able to do this. Idealism is therefore inferior to realism, which offers a straightforward explanation for the fact that even children see the moon in the right place. As Becher puts it, the hypothesis that the perceived objects are real things in themselves is an incomparably more powerful hypothesis [eine unvergleichlich leistungsfähigere Hypothese] than the idealist competitor (Becher, 1926b, p. 13). I read this as an argument for dismissing idealism and accepting realism, because realism offers the best explanation for our sequence of perceptions.Footnote 31
An alternative to Becher’s realism
As we have seen, Becher dismisses certain idealist positions because they are not able to explain the series of our perceptions as well as the realist hypothesis that there are real external objects. It will be instructive to look more closely at another theory that cannot be so easily dismissed in the context of Becher’s inductive metaphysics. It is a theory brought forward by Bertrand Russell. Although it falls in a similar period to Becher’s writings, Becher does not seem to have been aware of it. Russell’s theory is also an interesting case of contrast because, as we will see below, it is a theory Reichenbach contrasts with his own account of realism.Footnote 32
Russell’s theory can best be introduced as an improvement of a theory Becher does discuss: Becher considers the idea that objects are mere perceptual possibilities, a theory he attributes to John Stuart Mill and ultimately traces back to George Berkeley (Becher, 1921, p. 94). According to this theory, there are no real objects, but only our perceptions and certain perceptual possibilities that can become actual. For example, the wall behind my back, which I do not perceive right now, is a perceptual possibility that becomes actual as soon as I turn around. Becher’s objection against this theory is that it does not accomplish what is required: what is not real, but merely an unrealized possibility, cannot have a causal effect, thus cannot be embedded in an actual causal nexus. The postulation of such mere perceptual possibilities can thus contribute nothing to considering the course of the world as a course governed by actual laws (Becher 1922, p. 94).Footnote 33
Bertrand Russell’s version of phenomenalism, which he advocates in several writings,Footnote 34 can be seen as an improvement of the theory of mere perceptual possibilities. Russell’s initial aim is to construct the objects of physics out of sense-data (1918 , p. 146). By sense-data he means the immediate objects of our sensations, for example particular patches of color or particular noises (1918 , p. 147). But Russell recognizes that it is not possible to construct the objects of physics solely out of sense-data that are actually sensed.Footnote 35 For this reason, he introduces additional entities, which he calls “sensibilia”. Sensibilia are just like sense-data, only that they are not necessarily actually sensed (1918 , p. 148).Footnote 36 The appearances of an object can be divided into actual appearances (sense-data), and possible appearances (unsensed sensibilia). The objects of common sense are then defined as the class of their actual and possible appearances (1918 , p. 154).
The difference to a theory of mere perceptual possibilities consists in the claim that sensibilia are entities that exist independently of being sensed. This means that, ontologically speaking, the possible appearances of objects are actually existing sensibilia, which only are not actually sensed. In a way, then, Russell’s phenomenalism turns out to be a sophisticated form of realism, because Russell postulates the existence of sensibilia which are entities existing independently of being sensed by anyone.Footnote 37
There is a remarkable similarity between the ways Becher and Russell proceed when developing their respective theories. Just like Becher, who postulates real objects in order to expand the range of our perceptions to the overall picture of a world that follows certain comprehensible regularities, Russell postulates unsensed sensibilia in order to fill the gaps in our series of perceptions. And I think that Becher, had he become aware of Russel’s position, would have had to concede that it too offers an explanation for the series of our perceptions, albeit a different one. The pressing question, then, is how to decide between different possible explanations of the same data.
Russell, again like Becher, acknowledges that his theory is only a hypothesis which, just like the hypotheses of the sciences, cannot claim any certainty and can possibly be overthrown by further evidence or a better alternative in the future (Russell, 1918 , p. 158; 1926 , p. 103). It is also instructive to see what he brings forward as a reason for preferring his theory over the competing realist alternative: Russell refers to Occam’s razor as a principle to support his theory (Russell, 1918 , p. 155; 1926 , p. 112). The reasoning behind this is that the unsensed sensibilia postulated by Russell are entities of the same kind as sense-data, the only difference being that they are unsensed. Becher’s realism, on the other hand, postulates objects—things in themselves—which are of a completely different kind than the perceptions we have immediate access to. So Russell seems to claim that his hypothesis leads to a better explanation of the series of our perceptions because the hypothesis is simpler with regard to its general ontological commitments.Footnote 38
On the other hand, Becher could point out that things are not that clear: While Russell’s theory is simpler with regard to the types of postulated entities, the particular physical objects constructed from the sensibilia look much more complicated than the objects postulated by Becher. According to Russell’s theory, each physical object consists at any time t of infinitely many sensibilia, each of them representing a different potential perspective of a potential observer on the constructed object at that time (cf. Leerhoff, 2008, p. 131). Also, Russell has to go to great lengths to explain how the construction of the objects from sensibilia actually works, which adds to the impression that his theory is not that simple after all.Footnote 39 And if we accept simplicity as a criterion for ranking explanations,Footnote 40 it is not clear which of the two theories ranks better on this criterion.
To put it in a nutshell, I think this discussion shows that while Becher presents an interesting outlook on the basic idea of an argument for a realist ontology, it has to be said that many details have to be worked out for it to succeed. In particular, we need to work out concrete criteria for evaluating explanations in order to be able to weigh which explanation should be distinguished as the best (based on the current evidence). An obvious first step for this, in line with the basic idea of inductive metaphysics, would be to take a look at how explanations work in the sciences and to make a deep analysis of the way competing possible explanations are weighed in scientific practice.Footnote 41
The empirical-inductive method as the method of metaphysics
As we have seen, the empirical-inductive method of the natural sciences is a complex method which incorporates several different partial steps. It is an empirical method, because it builds on perceptions as its ultimate basis of knowledge. It is an inductive method, because it includes various forms of inductive reasoning (Inductive Generalization, Analogy, and Inference to the Best Explanation). But the name of the method must not hide the fact that it also contains deductive and a priori elements: The natural sciences also make considerable use of mathematical knowledge, which is not based on experience (Becher, 1926b, p. 17 f.). Becher also notes that besides inductive inferences, deductive inferences play an important role in the natural sciences: on the one hand, further more concrete laws are deductively derived from inductively inferred general laws. On the other hand, hypotheses that are not yet considered to be confirmed can be verified by deductively deriving consequences from them, which can then be tested on the basis of experience (Becher, 1926b, pp. 19–26). And last but not least, as we have seen above, the inductive inferences that allow us to transcend the realm of our own present consciousness content are based on presumptions that cannot be empirically justified. Even if they cannot be justified a priori either, Becher calls them a priori principles (Becher, 1914, p. 81; 1921, pp. 222–229; 1926b, p. 17), since they necessarily precede any empirical knowledge.
So that is the method of the natural sciences. The next question is how the method of metaphysics should be designed. Becher’s position on this is—in keeping with the basic idea of inductive metaphysics—that the empirical-inductive method just outlined should also be applied in metaphysics.
First of all, Becher is very critical of the a priori methods of classical metaphysics. The impression that metaphysics must follow an a priori method is, according to him, created by the fact that the total reality to be investigated in metaphysics far exceeds the limits of our experience (Becher, 1926b, p. 20). But, as he points out, none of the great metaphysical systems has ultimately proved tenable. Moreover, Becher notes that unacknowledged empirical elements have always been incorporated into the construction of these systems—the alleged a priori systems have never been completely free of empirical input (Becher, 1926b, p. 21). It is therefore time to officially admit empirical foundations also in metaphysics.
As he points out, the empirical-inductive method, which has proven itself in the natural sciences and has been used successfully for a long time, can also be applied in the field of metaphysics. The above analysis has shown that this method proves to be so powerful because it combines many different elements: First of all, perceptions as the ultimate basis of knowledge are also indispensable in metaphysics, simply because it is the only way in which we can have any contact at all with the reality that metaphysics seeks to explore (Becher, 1921, 323 f.; 1926b, p. 21). The fear that the limits of experience cannot be exceeded within the framework of the empirical-inductive method has already proved to be unfounded above. It has become clear that the natural sciences also rely on a priori elements and principles in their empirical-inductive method, especially in the form of a priori presumptions necessary for cognition. Thus, especially by using inferences to the best explanation, which are based on the presumption of regularity, the limits of experience can be transcended and insights can be gained in the area transcending immediate experience. The idea of inductive metaphysics is that this can be done in the same way within the framework of metaphysics (Becher, 1921, p. 324). The result is a metaphysics that can never be considered complete and whose results, because they are based on experience and on unprovable principles of cognition, can never be considered certain. However, these are points which also apply to the natural sciences and which do not prevent us from considering the enterprise as fruitful in this area. So they should not bother us in metaphysics either (Becher, 1926b, pp. 22–27).
In a way, we have already seen above an example of a metaphysical use of this methodFootnote 42: Although the question of realism occurs in the natural sciences and also in everyday life, it is certainly a metaphysical question because of its generality. The individual sciences determine the reality of certain entities, e.g. electrons, within the framework of their theories. The claim that there is, in fact, an external world with objects that are in a way that is independent of our way of perceiving them is a general observation that transcends the individual sciences and therefore falls within the realm of metaphysics.Footnote 43 At the same time this example also shows that the boundaries between metaphysics and the individual sciences are fluid.
With these points in mind, let us now take a look at Reichenbach’s position.