How can we think in a language?

Already in antiquity, language was accorded a prominent role in our mental lives. An early point of contention, however, was whether we think in a natural language or in a mental language. In the 1970s, Fodor revived the debate by arguing that there must be an innate language of thought, which serves as the medium of all reasoning by means of proposition- bearing thoughts. Other theorists, inspired by the work of Vygotsky, argued that the languages we speak play an important role in the thought of an individual. According to Vygotsky, children acquire language in social interaction, yet in the course of development language becomes internalized (turning into inner speech), thereby adopting various cognitive functions. This position challenges us to explain how to best conceive of inner speech and the cognitive mechanisms underlying it, how it relates to spoken language, to thought and to other cognitive processes. In this project, we will take up this challenge and argue that spoken language is itself the medium of all propositional thought. To that end, two deeply entrenched assumptions need to be exposed and questioned. One is that language is essentially a tool by which speakers reveal to hearers the contents of underlying thoughts. If we say that, then we cannot maintain that the languages we speak are themselves the medium of propositional thought. The other is the assumption that all thought is propositional thought. If all thought were propositional thought and propositional thought were inner conversation, then there would be no kind of thought in terms of which we could explain language acquisition and the processes of deciding what to say and how to react to what is said to us. In addition, we need to explain how cognitive processes can be conceived as the internalization of interpersonal language. This requires us to develop a model of intrapersonal communication that admits the possibility of informative and guiding uses of inner speech. This will involve developing a conception of speech production and speech consumption, in both interpersonal and intrapersonal contexts, that grounds these functions in modes of cognition that do not themselves consist in inner speech. Further, we must explicate the relation between inner speech and overt speech, inasmuch as inner speech need not be articulated to the same extent as overt speech. And we must explicate the relation between inner speech and auditory imagery (the imagined sound of a voice), inasmuch as inner speech, if it is the medium of all propositional thought, cannot always be conscious. In sum, this project promises to greatly advance our understanding of how language and cognition relate to one another and how language shapes our cognitive architecture.