 Avicenna investigates five main types of hypothetical syllogisms (with further internal divisions). The first three are combinations of two conditional premises (type 1), a conditional premise and a disjunctive premise (type 2), or two disjunctive premises (type 3), and are called pure (ṣirfa) hypothetical syllogisms. The last two are combinations of a conditional and a categorical premise (type 4, subdivided into two classes), or of a disjunctive and a categorical premise (type 5), and are called mixed (muḫtalaṭa) hypothetical  syllogisms.[16]