In my work on Hume’s account of cognition, I discovered that many objections to Hume depend on the (tacit) assumption of certain strong parallels between mind and language. Specifically, the objections frequently relied on the assumption that the grammatical structure of a bit of language which describes or expresses a given mental state will mirror the psychological structure of that state. Since Hume does not accept the view that one can simply read off a mental state’s psychological structure directly from the grammatical structure of those related bits of language, many of these objections would not be particularly worrisome to Hume. Or at least, that is what I argued. I’ve taken to calling this view (which is rejected by Hume, but implicitly accepted by some of his detractors) “the Mirror Thesis”.
I’ve since become interested in the more general role of this purported parallelism between mental and linguistic structures in the thinking of early modern philosophers, and was quite pleased to come across a statement in Leibniz’s New Essays on this very point:
THEO: […]I really believe that languages are the best mirror of the human mind, and that a precise analysis of the significations of words would tell us more than anything else about the operations of the understanding. (NE, 333)
Obviously, this quote, all by itself, doesn’t really tell us what Leibniz’s views are specifically, since there are many ways of cashing out this mirror analogy. Nevertheless, Leibniz, here, is clearly endorsing some version of a mirror thesis.
For context, this comes in Leibniz’s discussion of 3.7 of Locke’s essay (“Of Particles”), which contains a frustratingly compressed presentation of some of the most interesting elements of Locke’s philosophy of language.