of causation (ever since Hume), according to which causation involves uniformity or necessary connection according to law. In the next section I will show that Isaac Newton defended a view that, though similar qua basic insights, was even more radical than Locke's. Whereas it was Locke's view that the idea of causation does not involve the idea of necessary connection according to law, Newton took the far more radical step of separating causation from law-like behavior. 3.2.2. Newton: rejection of the principle of causality In his masterpiece, Philosophiae Naturalis Principia Mathematica , Newton (1642-1727) set forth the mathematical laws of physics and "the system of the world." The world system consists of material bodies (masses com-posed of "solid, massy, hard, impenetrable, moveable particles") at rest or in motion and interacting according to his three famous laws of motion, which are stated in implicitly causal terms: (1) Every body perseveres in its state of rest, or of uniform motion in a right line, unless it is compelled to change that state by forces impressed thereon. (2) The alteration of motion is ever proportional to the motive force impressed; and is made in the direction of the right line in which that force is impressed. [8] (3) To every Action there is always opposed an equal Reaction; or the mutual actions of two bodies upon each other are always equal, and directed to contrary parts. (Newton [1687] 1968, I: 19-20) The meaning of his implicit reference to causation in expressions such as