 Ockham was the first philosopher to develop in some detail the notion of “mental language” and to put it to work for him. Aristotle, Boethius and several others had mentioned it before, but Ockham’s innovation was to systematically transpose to the fine-grained analysis of human thought both the grammatical categories of his time, such as those of noun, verb, adverb, singular, plural and so on, and — even more importantly — the central semantical ideas of signification, connotation and supposition introduced in the previous  section.[22]  Written words for him are “subordinated” to spoken words, and spoken words in turn are “subordinated” to mental units called “concepts”, which can be combined into syntactically structured mental propositions, just as spoken and written words can be combined into audible or visible sentences.