Hume describes his Treaties as an achievement that would bring about revolutionary changes in philosophy. In this paper, I focus on his theory of causation and show that it is an attempt to accomplish a revolution not only in epistemology but also in metaphysics. In opposition to the traditional conceptual setting, which locates the concept of causation in the domain of knowledge, Hume locates it in the domain of probability. In this sense, his theory of causation is a revolution in epistemology. Rejecting every existing account of causal power, Aristotelian, Scholastic, and Cartesian, all of which take causal power to reside in some objects or other, Hume maintains that it resides in the mind that, having observed the constant conjunction between two kinds of objects, passes from the idea of one object to its usual attendant. In this sense, his theory of causation is a revolution in metaphysics.