四因说（four causes），由古希腊哲学家亚里士多德提出，将世界上事物的变化与运动的背后原因（古希腊语：αἴτιον）归纳为四大类。四因包括：

亚里士多德认为，凡感性实体，包括自然物和人造物，都具备这四种原因。

"Four causes" refers to an influential principle in Aristotelian thought whereby explanations of change or movement are classified into four fundamental types of answer to the question "why?" Aristotle wrote that "we do not have knowledge of a thing until we have grasped its why, that is to say, its explanation." While there are cases where classifying an explanation is difficult, or in which classes of explanation might merge, Aristotle was convinced that his four classes of explanation provided an analytical scheme of general applicability.