 Consider a case that is in important respects analogous to what we are examining here. Suppose that a flash of lightning has caused a brush fire. A drought, let us say, had left the brush dry, and had this not been so, the lightning flash would not have caused the fire, or at least would have been less likely to do so. Now suppose that the dryness of the brush is cited as an explanation of the flash’s causing the fire. Does the truth of the proffered explanation hinge on whether the fire has a certain feature, and can the explanation be true even if the brush’s being dry did not cause either the flash, the fire, or the flash’s causing the fire? Apparently not.