Aristotle held that a proposition involves two terms, a subject and a predicate. Propositions can be universal ("all," "no") or particular ("some"), and affirmative or negative. Aristotle's formal logic was confined to examination of syllogisms, which consist of three propositions. The first two are the premises, and must share only one term. The third proposition is the conclusion, which contains the two terms that are not shared by the premises. Aristotle also investigated how the common term (shared by the two premises) can occur and the effects of its different ways of occurring. Aristotle's work on syllogisms bears interesting comparison with the Indian schema of inference and the less rigid Chinese discussion.