  Aristotle’s non-modal syllogistic (Prior Analytics A 1–7) is the pinnacle of his logic. Aristotle defines a syllogism as ‘an argument (logos) in which, certain things having been laid down, something different from what has been laid down follows of necessity because these things are so’. This definition appears to require (i) that a syllogism consists of at least two premises and a conclusion, (ii) that the conclusion follows of necessity from the premises (so that all syllogisms are valid arguments), and (iii) that the conclusion differs from the premises. Aristotle’s syllogistic covers only a small part of all arguments that satisfy these conditions.