One of Ockham's fundamental tenets about the human intellect is that its acts constitute a mental language. Although this language of thought shares some of the features of conventional language, thought is commonly considered as prior to conventional language. This paper tries to show that this consensus is seriously challenged in Ockham's early writings. I shall argue that, in claiming the priority of conventional language over mental language, Ockham established a novel explanation of the systematicity of thought—an explanation which anticipates (...) the idea that thought becomes systematic through the acquisition of conventional language. (shrink)