Causation: The fundamental kind of relation expressed by such terms as produce, originate, and bring about. The items related (cause and effect) may be persons, objects, states of affairs or events. Aristotle recognized four types of causality: efficient, final, formal and material. David Hume famously tried to analyze causality as a constant conjunction between different types of events. Philosophers such as Thomas Reid have argued for a fundamental type of causation known as “agent causality,” in which persons (not merely events occurring in persons) bring about effects. Important philosophical disputes in this area include debates about determinism (Are all events causally determined, or do persons sometimes possess free will?) and about the principle of sufficient reason, which in some forms holds that all events (at least of a certain type) or all contingent substances must have a cause. This principle plays a key role in cosmological, or first cause, arguments for God’s existence.1