Why Morphology?

For quite a while now, I’ve been wondering why natural language (NL) has so much morphology.  In fact, if one thinks about morphology with a minimalist mind set one gets to feeling a little like I. I. Rabi did regarding the discovery of the muon. His reaction? “Who ordered that?”.  So too with morphology; what’s it doing and why is there both so much of it in some NLs (Amer-Indian languages) and so little of it in others (Chinese, English)? One thing seems certain, look around and you can hardly miss the fact that this is a characteristic feature of NLs in spades!!

So what’s so puzzling? Two things. First, it’s absent from artificial languages, in contrast to, say, unbounded hierarchy and long distance dependency (think operator-variable binding). Second, it’s not obviously functionally necessary (say to facilitate comprehension). For example, there is no obvious reason to think that Chinese or English speakers (there is comparatively little morphology here) have more difficulty communicating with one another than do Georgian or Athabaskan speakers, despite the comparative dearth of apparent morphology. In sum, morphology does not appear to be conceptually or functionally necessary for otherwise we (I?) might have expected it to be even more prevalent than it is. After all if it’s really critical and/or functionally useful then one might expect it to be everywhere, even in our constructed artificial languages.  Nonetheless, it’s pretty clear that NLs hardly shy away from morphological complexity.

Moreover, it appears that kids have relatively little problem tracking it. I have been told that whereas LADs (language acquisition devices, aka: kids) omit morphology in the early stages of acquisition (e.g. ‘He go’), they don’t produce illicit “positive” combinations (e.g. ‘They leaves’). I have even been told that this holds true for languages with rich determiner systems and noun classes and fancy intricate verbal morphology: it seems that kids are very good at correctly classifying these and quickly master the relevant morphological paradigms.  So, LADs (and LASs; Language Acquisition Systems) are good at learning these horrifying (to an outsider or second language learner) details and at deploying them effectively as native speakers. So, again, why morphology?

Unburdened by any knowledge of the subject matter, I can think of four possible reasons for morphology’s ubiquity within NLs. I should add that what follows is entirely speculative and I hope that this post motivates others to speculate as well. I would love to have some ideas to chase down. So here goes.

The first possibility is that visible morphology is a surface manifestation of a deeper underlying morphology. This is a pretty standard Generative assumption going back to the heyday of comparative syntax in the early 80s. The first version of this was Jean-Roger Vergnaud’s (terrific) theory of abstract case. The key idea is that all languages have an underlying abstract case system that regulates the distribution of nominal expressions.  If we further assume that this abstract system can be phonetically externalized, then the seeds of visible morphology are inherent in the fundamental structure of FL. The general principle then is that abstract morphemes (provided by UG) are wont to find phonetic expression (are mapped to the sensory and motor systems (S&M)), at least some of the time.

This idea has been developed repeatedly. In fact, the following is still a not an unheard of move: We find property P in grammar G overtly, we then assume that something similar occurs in all Gs, at least covertly. This move is particularly reasonable in the context of “Greed” based grammars characteristic of early minimalism. If all operations are “forced” and the force reduces to checking abstract features, then using the logic of abstract case theory, we should not be surprised if a G_L expresses these phonetically.

Note that if something like this is correct (observe the if), then the existence of overt morphology is not particularly surprising, though the question remains of why some Gs externalize these abstracta and some remain phonetically more mum.  Of late, however, this Greed based approach has dimmed somewhat (or at least that’s my impression) and generate and filter models of various kinds are again being actively pursued. So…

A second way to try and explain morphology piggy-backs on Chomsky’s recent claims that Gs are not pairings of sound and meaning but pairings of meanings with sound. His general idea is that whereas the mapping from lexical selection to CI is neat and pretty, the externalization to the S&M systems is less straightforward. This comports with the view that the first real payoff to the emergence of grammar was not an enhancement of communication but a conceptual boost expanding the range of cognitive computations in the individual, i.e. thinking and planning (see here). Thus externalization via S&M is a late add-on to an already developed system. This “extra” might have required some tinkering to allow it to hook onto the main lexicon-to-CI system and that tinkering is manifest as morphology. In effect then, morphology is family related to Chomsky and Halle’s old readjustment rules.  From where I sit, some of the work in Distributed Morphology might be understood in this way (it packages the syntax in ways palpable to S&M), though, I am really no expert in these matters so beware anything I say about the topic. At any rate, this could be a second source for morphology, a kluge to get Gs to “talk.”

I can think of a third reason for overt morphology that is at right angles to these sorts of more grammatically based considerations. There are really two big facts about human linguistic facility: (i) the presence of unbounded hierarchical Gs and (ii) the huge vocabulary speakers have.  Though it’s nice to be able to embed, it’s also nice to have lots of words.  Indeed, if travelling to a foreign venue where residents speak V and given the choice of 25 words of V plus all of G_V or 25,000 words of V plus just the grammar of simple declaratives (and maybe some questions), I’d choose the second over the first hands down. You can get a lot of distance on a crappy grammar (even no grammar) and a large vocabulary.  So, here’s the thought: might morphology facilitate vocabulary development?  Building a lexicon is tough (and important) and we do it rapidly, very rapidly. Might overt morphology aid this process, especially if word order in a given language (and hence PLD of that language) is not all that rigid?  It could aid this process by providing stable landmarks near which content words could be found. If transitional probabilities are a tool for breaking into language (and the speech stream, as Chomsky proposed in LSLT and later rediscovered by Aislin, Saffran and Newport), then having morphological landmarks that probabilistically vary at different rates than the expressions that sit within these landmarks then it might serve to focus LADs and LASs on the stuff that needs learning; content words. On this story, morphology exists to make word learning easier by providing frames within a sentence for the all-important lexical content material.

There is a second version of this kind of story that I would like to end with. I should warn you that it is a little involved. Here goes. Chomsky has long identified two surprising properties of NLs. The first is unbounded hierarchical recursion, the second is our lexical profligacy. We not only can combine words but we have lots of words to combine. A typical vocabulary is in the 50,000 word range (depending on how one counts). How do we do this. Well, assume that at the very least, each new vocabulary item consists of some kind of tag (i.e. a sound or a hand gesture). In fact, for simplicity say that acquiring a word is simply tagging it (this is Quin’s “museum myth,” which like many myths may in fact be true). Now this sounds like it should be fairly easy, but is it?  Consider manufacturing 50,000 semantically arbitrary tags (remember, words don’t sound the way they do because they mean what the do, or vice versa).  This is hard. To do this effectively requires a combinatoric system, Indeed, something very like a phonology, which is able to combine atomic units into lexical complexes. So, assume that to have a large lexicon we need something like a combinatoric phonology and the products of this system are the atoms that the syntax combines into further hierarchically structured complexes. Here’s the idea: morphology mediates the interactions of these two very different combinatoric systems.  Meshing word structures and sentence structure is hard because the modes of combination of the two kinds of systems are different. Both kinds play crucial (and distinctive) roles in NL and when they combine morphology happens!  So, on this conception, morphology is not for lexical acquisition, but exists to allow words with their structures to combine into phrases with their structures.

The four speculations above are, to repeat, all very speculative and very inchoate. They don’t appear to be mutually inconsistent, but this may be because they are so lightly sketched. The stories are most likely naïve, especially so given my virtually complete ignorance of morphology and its intricacies. I invite those of you who know something about morphology to weigh in. I’d love to have even a cursory answer to the question.