 In the Prior Analytics, Aristotle presents the first system of logic, the theory of the syllogism (see the entry on  Aristotle’s logic  and ch. 1 of Lagerlund 2000 for further details). A syllogism is a deduction consisting of three sentences: two premises and a conclusion. Syllogistic sentences are categorical sentences involving a subject and a predicate connected by a copula (verb). These are in turn divided into four different classes: universal affirmative (a), particular affirmative (i), universal negative (e) and particular negative (o), written by Aristotle as follows: 