Scott Soames argues that linguistics and psychology are separate enterprises, since they differ in their domain of study and empirical discoveries in one are unlikely to be realized in the other. He does this primarily by identifying what sorts of things linguists are up to, and comparing that with what is properly psychological.
Soames says that linguistics and psychology are “conceptually distinct” (155) in the sense that they differ in their domain of study. In order to do this, he identifies what he calls the three “Leading Questions” (158) of the linguistic enterprise. They are questions concerned with the differences and similarities between actual natural languages, between natural languages and artificial or animal ones, and between languages and their historical variations. These are, according to Soames, the basic questions that define the domain of linguistics because they are the questions that initiate the actual practice of linguistics. It is these sorts of questions that linguists are out to answer.
Soames also highlights facts about linguistics which are clearly not psychological. For instance, semantics in linguistics requires a non-psychological component in the form of truth conditions. Truth conditions are essentially relations between sentences in a language, which may be thought of as abstract or mentalistic, and the real world. To use the famous example, ‘snow is white’ if and only if snow is white. While one can argue that ‘snow is white’ is a mentalistic object, it would be much more difficult to make the case that the fact that snow is white is psychological in nature. Hence, the case of truth conditions in semantics provides a counterexample for the claim that linguistics is entirely about the minds of language users, and hence the claim that linguistics is psychology falls apart. They must differ, at least somewhat, in their domains; some facts about language are linguistic and not psychological.
Soames also comes at the problem from the opposite side, noting that psychologists are concerned with things like the processing times and error rates between individuals speaking certain languages. These, while interesting facts for Soames, are not a part of linguistics proper. That is, theoretical linguistics is not concerned with mental aspects of human speech, but rather the output of the speakers, the language itself. Because there are things that psychologists are concerned with that linguists need not be, the domain again seems to be different. Some facts about language users are psychological and not linguistic.
In short, for Soames, linguistics is about languages as abstract objects, while psychology is about language users.
Soames’ second major claim is that linguistics and psychology are “empirically divergent” (155), that is, empirical investigation of language speakers is unlikely to discover that the grammars posited by linguists “correspond exactly” (168) with the mental structures of competent speakers.
To make this case, Soames notes that while some linguistic facts can correspond to psycholinguistic ones (such as the case of grammatical sentences and competent speakers judging sentences to be grammatical), others will not correspond. Instead, there are facts that only one discipline (between linguistics and psychology) will be interested in. Psycholinguistic data will be of interest to psychologists, but not to theoretical linguists. Meanwhile, semantic facts of truth conditions, logical properties and relations (169) will be of interest only to linguists. In formulating their theories, each discipline has its own epistemological domain as well, the domain of empirical facts that are to be admitted into the theory-forming process.
Despite this diversity, there is a logical possibility that the linguistic theory of grammar and the psychological theory of competence will turn out to be isomorphic after all; the theory of grammar may indeed correspond 1:1 to a psychologically real structure, however unlikely this is to Soames. But to say that linguistic theories are psychological in nature is to assume in advance that such theories do correspond. It would be an empirical discovery that an isomorphism exists between a grammar and a competence model.
Soames again appeals also to the actual practices of linguists, noting that linguists aim to produce a theory of grammar that is as simple and general. Again, it may be that the psychologically real model of competence is optimally simple and general, but this cannot be assumed. There is no reason to suppose that things will turn out this way. Hence, to suppose that building a minimalistic and general theory of grammar is the proper means of building a theory of competence is ill-conceived.
Because counting linguistic models as psychological ones rests on epistemologically dubious assumptions, which he thinks are unlikely to be the case, Soames argues that linguistics cannot properly be thought of as a psychological enterprise.
Does Soames beg?
Soames’ criterion of demarcation between the linguistic and the non-linguistic rests on the Leading Questions of linguistics. Soames takes these definitionally as what linguistics is about, which seems to beg the question.
Further, Soames also says that “nothing [linguistic] logically follows” (159) from certain facts about processing times and grammatical mistakes between speakers of different expression types. This is based on the assumption that languages are abstract entities and that linguistics is about them. If, on the other hand, one takes the position that languages are mentalistic in nature, Soames’ reasoning doesn’t seem to work.
A bit of ontology
Soames frequently refers to the facts that linguists and psychologists rely on. One might wonder whether these facts are all mentalistic in nature if they are meant to be separate from states of affairs. He also says that truth conditions are at least partly about non-psychological facts. How a theory of truth is to work, however, is no simple matter. A coherence theory of truth, however implausible, would not rely on a correspondence with an external reality but rather with how they logically cohere with other beliefs the speaker has—both elements thus being mental states. Pragmatic theories of truth might suffer from similar struggles.
Soames, Scott. ‘Linguistics and Psychology’. Linguistics and Philosophy 7 (1984). 155–179.