This article is the result of research on the occurrences of the terms suppositio, supponere and their linguistic derivations in the literature on fallacies of the second half of the thirteenth century. The authors analysed are Albert the Great, Giles of Rome, Simon of Faversham, the so-called Incerti Auctores, the Anonymous of Prague and John Duns Scotus. The central elements that emerge are the role played by the notion of suppositum and by the linguistic context to determine the denotation of (...) an expression, and the importance of the metaphysical problem of the unity and identity of suppositum in both the theory of predication and the theory of inference. Both subjects, obviously, are closely connected. (shrink)