 Birth control pills directly promote thrombosis, but at the same time, they prevent pregnancy, which itself promotes thrombosis. By adjusting the probabilities, we can make it so that, overall, taking birth control makes no difference to the probability of thrombosis. Then, we might be inclined to accept the type causal claim “birth control pills have no effect on thrombosis”—after all, your chances of getting thrombosis are exactly the same, whether or not you take birth control. Hitchcock (2001b) argues that cases like this require us to distinguish two different kinds of effects which type causes can have: what he calls a net effect, on the one hand, and what he calls component effect, on the other. In Hesslow’s case, birth control pills have no net effect on thrombosis. This is the sense in which it’s true to say “birth control pills have no effect on thrombosis”. At the same time, birth control pills have a component—or path-specific—effect on thrombosis. Along the path B → T, birth control promotes thrombosis. This is the sense in which it’s true to say “birth control pills cause thrombosis”. For further discussion, see Woodward (2003: §2.3) and Weinberger (2019).