The term morpheme was coined by Jan Baudouin de Courtenay in 1880, and has become widely known through its use in Bloomfield’s Language (1933). However, it has not been used consistently over the years. The inconsistent usage was described in some detail by Mugdan (1986) for the first hundred years of the term’s existence,Footnote 4 and the situation has not improved since then. Carstairs-McCarthy (2005: 22) suggests that perhaps “the term ‘morpheme’ has hindered rather than helped our understanding of how morphology works”. The term has been used in one of the three senses in (8), which are often not properly distinguished.
- (8)
- a.
morpheme 1:
a minimal form (= a morph)
- b.
morpheme 2:
a set of minimal forms with identical syntacticosemantic content
(= a set of homosemous minimal forms, see n. 4)
- c.
morpheme 3
a minimal element of (morpho-)syntactic representation
The first sense can be found in definitions of types of morphs, like affix and root (as seen in the preceding section), but it is also widely found elsewhere in the literature. When a linguist needs to refer to a minimal form outside of morphological theorizing, they are very likely to call it morpheme. Thus, the first sense could be described as the non-technical (or colloquial) sense of the term.
The second sense is quite prominent in the literature dealing specifically with morphology, and often appears in discussions of “allomorphs”, e.g.
- (9)
- a.
“Allomorphy is the phenomenon that a morpheme may have more than one shape.” (Booij 2005: 31)
- b.
“Variant forms of the same morpheme are called allomorphs.” (Kroeger 2005: 289)
For example, Kroeger (2005: 288-289) lists pairs of “allomorphs” such as these:
- (10)
Each of these examples shows two different affixes that have the same syntacticosemantic content (the same grammatical meaning, or the same morphosyntactic features; we can also say that they are homosemous).Footnote 5 Kroeger treats them as “allomorphs” of the same morpheme, and this usage is not uncommon (see §8 below). The morpheme in this sense is thus an abstract entity: it is not a form, but a set of minimal forms (in other words, a set of morphs) (this set-based definition is the one used by Hockett 1947: 322, and it is also very clear in the detailed discussion provided by Mel’čuk 2006: 384–397).
If one uses the term in this second sense, one can no longer felicitously say that a morpheme has a certain shape (e.g. “the morpheme -i”), or that some meaning is expressed by a morpheme, or that a word is divided into morphemes, or that several morphemes occur in a certain order, because the morpheme in this sense is not a concrete form. Of course, linguists say these things all the time, but when they do, they necessarily use “morpheme” in sense 1 (i.e. in the sense of ‘morph’). But this sense is incompatible with sense 2, and it is not coherent to say at the same time that a morpheme has a concrete shape and that it has several different “allomorphs” (like -en/-ed in English, cf. (10b)). Thus, one has to choose between one of the meanings if one wants to use consistent terminology.Footnote 6
Since it is identical syntacticosemantic content that is shared by the forms, some authors call this content itself the morpheme, as in the following quotation:
“Clearly the past tense form of loved consists of two morphemes, the verb-stem love and a grammatical morpheme which we can call Past, and it’s not too hard to draw a line between them. But the past-tense form took must likewise consist of two morphemes, the verb-stem take and the morpheme Past, yet this time we can’t draw a neat line at all: the two morphemes are just wrapped up in a single bundle, and we have to appeal to a more abstract level of representation to show that took is really take plus Past.” (Trask 1999)
Such “abstract morphemes” (“minimal elements of (morpho-)syntactic representation”, sense 3 above) have recently become prominent in the Distributed Morphology (DM) tradition, following Halle and Marantz (1993), and Embick’s (2015) general book about DM is titled The morpheme. As Mugdan (1986: 36) notes, the notion of abstract morphemes actually goes back to the 1960s (e.g. Bierwisch 1967; Chomsky 1965). In the 1960s and 1970s, they were often alternatively called “formatives”, but this term seems to have largely gone out of use.
To summarize, traditions that use the term “morpheme” can treat the two English plural forms book-s and ox-en in three different ways: They can say (i) that -s and -en are two different (but homosemous) morphemes expressing plural meaning (sense 1), (ii) that -s and -en are members of the same English morpheme (sense 2; designated {Plural}, or {-s, -en}, using curly brackets for sets), or (iii) that there is an abstract morpheme [plural] that may be realized by different exponents (-s and -en) (sense 3).
Because of this multiplicity of meanings of the term “morpheme”, I do not think that the term can be salvaged for future use in technical contexts. It will no doubt continue to be used colloquially (mostly in sense 1), but it seems best to avoid it in technical usage if one wants to be understood more widely. In its colloquial sense, it can be easily replaced by morph by authors who value precision and a broad readership.
We began in §2 with definitions of the terms affix (which is the basis for suffix and prefix) and root. Having simple definitions of these is important, because the terms suffix and prefix are very widely used, and in fact my original motivation for writing this paper was that I was very dissatisfied with many of the definitions of these commonly used terms in the literature.
Could one perhaps define an affix as a kind of “morpheme” in sense 2 or 3 in (8)? It seems clear that the answer is no, because we would not want to say that there is a “Korean suffix -i/-ka”, implying that -i is the same suffix as -ka, or that English has “a suffix -en/-ed” (whereas we could say that -i and -kabelong to the same morpheme {Nominative}, in sense 2, or that they realize the same abstract morpheme [nom], in sense 3).Footnote 7 Thus, affixes and roots are generally understood as special kinds of morphs, not as “morphemes” (unless one uses this term in sense 1, to refer to morphs).