The two first parts of the third (and last) treatise of Summa logicae echo Aristotle’s Analytics. Ockham is here involved in a systematic study of syllogisms ; he makes use of a lot of examples and proposes an appraisal of the validity of the different syllogistic combinations. Besides, the treatise presents a proof theory which implies a metaphysics of the singular and contingent being, a conception of knowledge as direct contact with the known, and a purely logical view of necessity.