Baoyu (Brian) Dai

The language of thought hypothesis (LoTH) claims that thoughts are underpinned by language-like vehicles. A central motivation is that there is a relevant similarity between language and thought explained by LoTH. But how language-like is the language of thought? I argue that this question has no obvious answer—many candidate answers render LoTH trivial or false. Thus LoTH faces a similarity problem: the challenge of fleshing out the similarity between natural language and the language of thought. There are two promising solutions to this problem: conservatism and liberalism. Conservatism is the received view. It says the language of thought is similar to natural language only insofar as it features propositional contents. I challenge the received view by defending liberalism—the view that the language of thought can feature both propositional and non-propositional contents. Liberalism should be preferred on empirical and theoretical grounds. I conclude by showing liberalism has broader consequences for other philosophical issues, such as the nature of concepts, Frege’s Puzzle, and the possibility of non-propositional intentionality.