 Another debate concerned the nature of mental language, specifically whether it is conventional or natural (Gelber 1984; Panaccio 1996) Ockham had argued that thinking occurs in a universal language made of concepts acquired naturally, i.e. through natural relations of causality and similitude. All conventional languages used for human communication are subordinated to this mental language, which is shared by everyone. But Crathorn could not accept such a position because of his cognitive theory according to which there are only qualities in the mind. So there can be natural signs of extra-mental qualities. What about substance-terms (the equivalent of proper and common names), verbs, and syncategorems, i.e., logical particles and connectives such as ‘or’, ‘but’, ‘all’, and ‘if’? Accordingly, Crathorn argues that except for natural signs of qualities, no natural likeness in the mind can explain the signification of these terms. Mental language is therefore as conventional as spoken and written languages and is in fact derived from conventional languages (I Sent., q. 2; Cf. Panaccio 1996, Perler 1997, Robert 2009b and 2010b). Just as thought depends on the species or likenesses of external things, mental words are likenesses of conventional words and have exactly the same semantic properties. Depending upon which language(s) you learn to speak, your mental language will be a likeness of Latin, English, French, etc. This does not mean that we do not have natural representations of the external world, but these mental qualia do not form a language. Crathorn was the only thinker of his time to affirm that conventional words are prior to their mental counterparts. Meaning is first given by a community of speakers; mental language is simply the internalization of these spoken and written languages. When we think about the world with propositions and syllogisms, we always think in a conventional language or, more precisely, in its mental reflection.