This paper explores a variety of different versions of the thesis that natural language is involved in human thinking. It distinguishes amongst strong and weak forms of this thesis, dismissing some as implausibly strong and others as uninterestingly weak. Strong forms dismissed include the view that language is conceptually necessary for thought (endorsed by many philosophers) and the view that language is de facto the medium of all human conceptual thinking (endorsed by many philosophers and social scientists). Weak forms include the view that language is necessary for the acquisition of many human concepts and the view that language can serve to scaffold human thought processes. The paper also discusses the thesis that language may be the medium of conscious propositional thinking, but argues that this cannot be its most fundamental cognitive role. The idea is then proposed that natural language is the medium for non-domain-specific thinking, serving to integrate the outputs of a variety of domain-specific conceptual faculties (or central-cognitive “quasi-modules”). Recent experimental evidence in support of this idea is reviewed and the implications of the idea are discussed, especially for our conception of the architecture of human cognition. Finally, some further kinds of evidence which might serve to corroborate or refute the hypothesis are mentioned. The overall goal of the paper is to review a wide variety of accounts of the cognitive function of natural language, integrating a number of different kinds of evidence and theoretical consideration in order to propose and elaborate the most plausible candidate.

Those who assume domain specificity or conceptual modularity face Fodor’ Paradox (the problem of “combinatorial explosion”). One strategy involves postulating a metamodule that evolved to take as input the output of all other specialized conceptual modules, then integrates these outputs into cross-domain thoughts. It’ difficult to see whether this proposed metamodular capacity stems from language or theory of mind.

Thought uses meaning but not necessarily language. Meaning, in the form of a set of possible concepts and ideas, is a nonphysical reality that lay waiting for brains to become smart enough to represent these ideas. Thus, the brain evolved, whereas meaning was discovered, and language was invented – collectively – as a tool to help the brain use meaning.

The hypothesis in the target paper is that the cognitive function of language lies in making possible the integration of different types of domain-specific information. The case for this hypothesis must consist, at least in part, of a constructive proposal as to what feature or features of natural language allows this integration to take place. This commentary suggests that the vital linguistic element is the relative pronoun and the possibility it affords of forming relative clauses.

Although Carruthers’ proposals avoid some of the more obvious pitfalls that face analysts of the language-cognition relationship, they are needlessly complex and vitiated by his uncritical acceptance of a highly modular variety of evolutionary psychology. He pays insufficient attention both to the neural substrate of the processes he hypothesizes and to the evolutionary developments that gave rise to both language and human cognition.

Carruthers has proposed a novel and quite interesting hypothesis for the role of language in conceptual integration, but his treatment does not acknowledge work in cognitive science on metaphor and analogy that reveals how diverse knowledge structures are integrated. We claim that this body of research provides clear evidence that cross-domain conceptual connections cannot be driven by syntactic processes alone.

Carruthers’ argument depends on viewing logical form as a linguistic level. But logical form is typically viewed as underpinning general purpose inference, and hence as having no particular connection to language processing. If logical form is tied directly to language, two problems arise: a logical problem concerning language acquisition and the empirical problem that aphasics appear capable of cross-modular reasoning.

Language isn't the only way to cross modules, nor is it the only module with access to both input and output. Minds don't generally work across modules because this leads to combinatorial explosion in search and planning. Language is special in being a good vector for mimetics, so it becomes associated with useful cross-module concepts we acquire culturally. Further, language is indexical, so it facilitates computationally expensive operations.

Peter Carruthers correctly argues for a cognitive conception of the role of language. But such a story need not include the excess baggage of compositional inner codes, mental modules, mentalese, or translation into logical form (LF).

Carruthers invokes a number of controversial assumptions to support his thesis. Most are questionable and unnecessary to investigate the wider relevance of language in cognition. A number of research programs (e.g., interactionist psycholinguistics and cognitive linguistics) have for years pursued a similar thesis and provide a more empirically grounded framework for investigating language’ cognitive functions.

We argue that natural language has the right degree of representational richness for false belief reasoning, especially the complements under verbs of communication and belief. Language may indeed be necessary synchronically for cross-modular reasoning, but certain achievements in language seem necessary at least diachronically for explicit reasoning about false beliefs.

In Carruthers’ formulation, cross-domain thinking requires translation of domain specific data into a common format, and linguistic LF thus plays the role of the common medium of exchange. Alternatively, I propose a process-oriented characterization, in which there is no common representation and cross-domain thinking is rather the process of establishing mappings across domains, as in the process of analogical reasoning.

Carruthers’proposals would seem to implicate language in what is known as System 2 thinking (explicit) rather than System 1 thinking (implicit) in contemporary dual process theories of thinking and reasoning. We provide outline description of these theories and show that while Carruthers’characterization of non-verbal processes as domain-specific identifies one critical feature of System 1 thinking, he appears to overlook the fact that much cognition of this type results from domain-general learning processes. We also review cognitive psychological evidence that shows that language and the explicit representations it supports are heavily involved in supporting System 1 thinking, but falls short of supporting his claim that it is the medium in which domain-general thinking occurs.

Carruthers suggests that natural language, in the form of inner speech, may be the vehicle of conscious propositional thought, but he argues that its fundamental cognitive role is as the medium of cross-modular thinking, both conscious and nonconscious. I argue that there is no evidence for nonconscious cross-modular thinking and that the most plausible view is that cross-modular thinking, like conscious propositional thinking, occurs only in inner speech.

Carruthers labels as “too strong” the thesis that language is necessary for all conceptual thought. Languageless creatures certainly do think, but when we get clear about what is meant by “conceptual thought,” it appears doubtful that conceptual thought is possible without language.

Four extensions of Carruthers’ arguments are given. (1) Specifics of the Vygotskyan tradition can enhance his claims. (2) Linguistic relativity might be seen as variation in how logical form (LF) and phonetic form (PF)serve working memory. (3) Language aids intermodular thinking because it makes representations maximally visible. (4) Language for intermodular thinking is not hardwired but opportunistic.

Carruthers’ thesis is undermined on the one hand by examples of integration of output from domain-specific modules that are independent of language, and on the other hand by examples of linguistically represented thoughts that are unable to integrate different domain-specific knowledge into a coherent whole. I propose a more traditional role for language in thought as providing the basis for the cultural development and transmission of domain-general abstract knowledge and reasoning skills.

I will argue (contra Carruthers) that accepting natural language as the format of many of our thoughts should entail accepting a version of Whorfian relativism and that, rather than something to be avoided, evidence from bilingual cognition suggests that incorporating this idea into future research would yield further insights into the cognitive functions of natural language.

Cognitive mechanisms are based in organisms’biology, and results from biological studies suggest that there is unlikely to be a single mechanism for reorienting or for combining information across modules or domains. Rather, there are likely to be multiple, partly overlapping systems for accomplishing nearly all cognitive and behavioral goals, as is the case for biological mechanisms more generally.

Postulating a variety of mutually isolated thought domains for prelinguistic creatures is both unparsimonious and implausible, requiring unexplained parallel evolution of each separate module. Furthermore, the proposal that domain-general concepts are not accessible without prior exposure to phonetically realized human language utterances cannot be implemented by any concept-acquisition mechanism.