Compatibilism is the belief that free will and determinism are mutually compatible and that it is possible to believe in both without being logically inconsistent. The opposing belief, that the thesis of determinism is logically incompatible with the classical thesis of free will, is known as "incompatibilism".
Arthur Schopenhauer
Saying "there may be a person behind that door" merely expresses ignorance about the one, determined reality.
Compatibilism has much in common with "hard determinism", including moral systems and a belief in determinism itself.
Free will is the capacity or ability to choose between different possible courses of action.
A biker performing a dirt jump that, according to some interpretations, is the result of free will
A domino's movement is determined completely by laws of physics.
René Descartes
Thomas Hobbes was a classical compatibilist.