  These were his version of the Aristotelian categorical propositions, where \(X\) is the subject term and \(Y\) the predicate term. The terms \(X\) and \(Y\) could be complex, for example, \(X\) could be “Either \(u\) and not-\(v\), or else \(w\)”. For Boole such terms were not very complicated, at most a disjunction   of conjunctions of simple terms and their contraries, no doubt a reflection of the fact that natural language terms are not very complex.