LOGIC In fact, however, syllogistic is only a fragment of logic It deals only with inferences that depend on words like ‘all’ or ‘some’, which classify the premisses and conclusions of syllogisms, not with inferences that depend on words like ‘if’ and ‘then’, which, instead of attaching to nouns, link whole sentences As we shall see, inferences such as ‘If it is not day, it is A head of Aristotle attributed to Lysippus (fourth century bc) 122