 In his Syncategoreumata, Peter analyses the significative function of the word ‘is’. To a certain extent his findings are not confined to that term alone, but cover all verbs, in which the verb ‘is’ is always understood. The most remarkable feature about his discussion of ‘is’ is his focus on the notion of composition. What he is particularly interested in is the kinds of things affirmative propositions featuring that verb can refer to, in his words, the type of composition involved in such propositions.