occurred in the textbooks of medieval logicians. Hubien (1975,1977) did the same in recent articles and other modern logicians with interest in the history of their field of knowledge, or students of the history of logic with knowledge of modern achievements in this field, could be mentioned. For example, Trentman (1977:41) in his recent edition of Vincent Ferrer's Tractatus de Suppositionibus, 'Treatise on suppositions', elucidates Ferrer's theory of natural supposition with the aid of modern logic and points out that in some respects, for example, in the theory of irltensionality, modern theories have been developed with little more success. In the Middle Ages, semantics and logic were entirely interwoven. For, in the opinion of medieval philosophers, thought is enacted in language. This very same language consists of meaningful entities and those entities form propositions that may be used as premisses in argument. In their opinion, language and thought were both related to reality in a natural way (cf. De Rijk, 1977:233). This is also evident from Marsilius' works (cf., e.g., p. 54, n. 11-23). The semantical presuppositions oT the propositions that may be used in arguments, are analysed. This, indeed, is one of the contributions to logic by medieval logicians (cf. Moody, 1975:385).

Bos and Read present here two medieval treatises on concepts. These treatises were first unearthed by one of the editors in the course of a different project, namely the search for the origins of the notion of 'suppositio collectiva'. They appear to have attracted no attention since the middle of the fifteenth century. These are two of only three medieval treatises known to the editors explicitly devoted to discussion of concepts. That is not to deny that other works treat extensively of concepts among other matters. In the late fourteenth and fifteenth centuries it became increasingly common to devote single treatises to single matters-supposition, consequences, exponibles, obligations and so on. A more famous treatise on concepts is Peter of Ailly's Concepts, given a modern translation by Paul Spade. Peter's treatise was written in Paris in the early 1370s, and printed there and in Lyon several times in the 1490s. Thomas of Cleves' treatise was also written in Paris in the early 1370's, and that of Paul of Gelria some ten years later, if not in Paris then in Prague. Neither has been printed before. To preface the edition of the two texts, the editors provide an introduction discussing the origin of medieval conceptions of concepts and commenting in detail on the content of the two treatises. They also provide some biographical information on the authors and attempt to date and place their texts.