Every linguist knows the term “allomorph”, but we cannot agree on what it means. I will argue here that this is a terminological issue, not a substantive issue. Of course, we disagree on many substantive issues (and in particular, on strategic issues), but there is no reason to “disagree” on terminological issues – this is merely a matter of convenience, and just as we agree on the IPA, we could easily agree on morphosyntactic notation/terminology if we wanted.
The crucial observation here is that when we have two synonymous segment sequences of the expression plane, we sometimes say that they are variants of the same form, but in other cases, we say that they are different forms. For example:
(1a) bett(-er) and be- (in be-st) are variants of the same root
(1b) the English plural suffix -s is pronounced in three different ways: [-s], [-z], and [-ɪz]
(2a) some comparatives are formed by root suppletion: the root good is replaced by the root bett(-er)
(2b) German has different plural suffixes depending on the declension class: -e, -er, -en, or -s
Clearly, bett- and be- can be thought of as being the same form (if we allow for a phonological process deleting the -tt, which may be sensible). But good and bett- are not the same form – they are different roots, and also different forms (because a root is just a special type of form, namely a kind of minimal form that is not further analyzable).
In the case of good/bett-, it is quite normal to speak of suppletion, but morphologists also sometimes use this term for cases of affixes that show no phonological similarities (e.g. Carstairs 1988; Haspelmath 2002: §2.5; Paster 2009). Thus, in the same way as it would be weird to say that good and bett- are “the same root” or “the same form”, it is also quite strange to say that the German plural suffix -e is “the same suffix” as -er. They have the same meaning/function (or in other words, they expone the same feature). On the other hand, it would be weird to say that English [-s], [-z], and [-ɪz] represent “three different plural suffixes”.
Thus, there is really very broad consensus in the discipline of linguistics that some sets of elements “are the same form”, while other sets of elements “are different forms”. What we do not agree on is how exaxctly to identify the two categories. While some linguists will regard bett-/be- as the same root (e.g. Bobaljik 2012), others will find the -tt deletion process too irregular and will regard them as two different suppletive forms, just like good/bett-. This is a substantive question, which I leave aside here. (It has been with us for hundreds of years, and I do not know how to resolve it.)
But the terminological issue can be resolved, as we have a very broad consensus in the field that sometimes, we are dealing with variants of the same form, while at other times, we are dealing with different forms:
– We can refer to sets of minimal elements that represent the same form as morph variants.
– And we can refer to sets of forms that have the same meaning/function (or that expone the same feature value) as suppletive morph sets.
Thus, the English plural elements [-s], [-z], and [-ɪz] are morph variants (they are variants of the same plural suffix), while the German plural suffixes -e, -er, -en, and -s are suppletive morph sets. They all mark plural on nouns, but they are different suffixes.
This is a perfectly clear terminological solution, which I argued for in a recent methodological paper (“The morph as a minimal linguistic form”). But where does this leave the traditional term “allomorph”?
There are two serious (and I believe fatal) problems with this traditional term:
First, “allomorph” is typically associated with “morpheme” (because one often talks about “several allomorphs of a morpheme”), but it is widely known among morphologists that this term is used in a variety of confusingly different ways by different people (cf. Mugdan 1986; 2015), and that many or most morphologists reject the “morpheme” (in whatever sense) (cf. Anderson 2015).
Second, it is unclear whether allomorphs are morph variants or suppletive morph sets. Are English [-s], [-z], and [-ɪz] allomorphs? (of a “morpheme” /s/?) Or are German -e, -er, -en, and -s allomorphs? (of a “morpheme” [PLURAL]?). Considering existing use, both answers are correct, but as we saw earlier, they cannot be both correct, because this would lead to contradictions or very odd statements (e.g. that there are “three different plural suffixes [-s], [-z], and [-ɪz]” in English). So the term allomorph is used in two different senses in the discipline, which are similar but incompatible, and this can only be remedied by giving it up.
The inconsistent usage is illustrated nicely by the results of a Twitter poll that I carried out recently. More than 80% of those who voted seem to understand “allomorphy” in the sense of morph variants:
But interestingly, the remaining 20% of the respondents understand “allomorphy” in the sense in which it is mostly used in the research literature. For example, Bonet & Harbour (2012: §2) distinguish “true allomorphy” (like good/bett-, or -en/-s for the English plural) from phonologically caused alternatives (and a range of other phenomena). I was somewhat surprised by the results of the survey, even though I had informally observed that the morphology textbooks seem to understand allomorphy differently from the research literature. The respondents are probably mostly “average linguists” with no special interest in cutting-edge ideas of morphology, and they tend to understand “allomorphy” in the sense of morph variants, not in the sense of suppletive morph sets. (Bonet & Harbour themselves note that textbook authors such as Matthews and Spencer tend to use “allomorphy” primarily in the “morph variant” sense (2012: §4.1); but it doesn’t occur to them that their sense of “allomorphy” may not be the “true” one.)
So we are dealing with a pernicious case of ambiguity of a technical-sounding term, and it would be good if linguists recognized this and shifted to different terms. Since we are used to the term “allomorph” and “allomorphy”, one might suggest alternative terms that sound more similar to them:
– supplemorph: for example, good and bett- are two supplemorphs that belong to the same suppletive set; one might also say that this is a case of supplemorphy.
– variomorphy: for example, one might say that the English plural suffix -s exhibits variomorphy, because there are several morph variants ([-s], [-z], and [-ɪz]); but note that one cannot call these “*variomorphs”, because they are variants of the same morph.
Many people don’t like new terms like these (for reasons I don’t understand), but in any event, it is important to realize that some of the most basic techical-sounding terms of our discipline are actually ambiguous and unclear, in a way that could be resolved, because the concepts are sufficiently clear and uncontroversial. Thus, there is hope!
Anderson, Stephen R. 2015. The morpheme: Its nature and use. The Oxford handbook of inflection, 11–33. Oxford: Oxford University Press.
Bobaljik, Jonathan David. 2012. Universals in comparative morphology: Suppletion, superlatives, and the structure of words. Cambridge, MA: MIT Press.
Bonet, Eulàlia & Harbour, Daniel. 2012. Contextual allomorphy. In Trommer, Jochen (ed.), The morphology and phonology of exponence, 195–235. Oxford: Oxford University Press.
Carstairs, Andrew. 1988. Some implications of phonologically conditioned suppletion. In Booij, Geert & van Marle, Jaap (eds.), Yearbook of morphology 1988, 67–94. Dordrecht: Foris.
Haspelmath, Martin. 2002. Understanding morphology. London: Arnold.
Haspelmath, Martin. 2021. The morph as a minimal linguistic form. https://ling.auf.net/lingbuzz/004926
Matthews, Peter H. 1974. Morphology. Cambridge: Cambridge University Press.
Mugdan, Joachim. 1986. Was ist eigentlich ein Morphem? Zeitschrift für Phonetik, Sprachwissenschaft und Kommunikationsforschung 39(1–4). 29–43. (doi:10.1524/stuf.1922.214.171.124)
Mugdan, Joachim. 2015. Units of word-formation. In Müller, Peter O. & Ohnheiser, Ingeborg & Olsen, Susan & Rainer, Franz (eds.), Word-formation: An international handbook of the languages of Europe, vol. Vol. 1, 235–301. Berlin: De Gruyter Mouton. (doi:10.1515/9783110246254-017)
Paster, Mary. 2009. Explaining phonological conditions on affixation: Evidence from suppletive allomorphy and affix ordering. Word Structure 2(1). 18–37. (doi:10.3366/E1750124509000282)
Spencer, Andrew. 1991. Morphological theory: An introduction to word structure in generative grammar. Oxford: Blackwell.