1. an event or state that brings about another (its effect).

2. in Aristotelian and rationalist philosophy, an entity or event that is a requirement for another entity or event’s coming to be. Aristotle proposed that there were four types of cause—material, formal, efficient, and final. In the case of a sculpture, for example, the material cause is the stone or metal from which it is made, the formal cause is the form or structure that it takes, the efficient cause is the sculptor, and the final cause is the sculptor’s aim or purpose in making it. —causal adj.