THE ARGUMENT

Here is a pattern of explanation we all accept, which was already met with in Section 3.4: “Why did the yogurt fail to ferment? It failed to ferment because none of the usual explanations of fermentation, namely, the presence of bacteria, were there to explain it, and there was no unusual cause. Why did the dog not bark? It did not bark because no stranger approached it and none of the other possible causes of barking caused it to bark.” These are perfectly fine explanations, and they are not elliptical for longer explanations, though of course they are not ultimate explanations since one may ask why no stranger approached the dog.

In these explanations, we explain a negative state of affairs by noting that the positive state of affairs that it is the denial of lacked an explanation. But now observe that this form of explanation presupposes a PSR, at least for positive states of affair, for if such a PSR does not hold, then one has failed to explain the negative state of affairs. If it is possible that a dog should bark without cause, then in saying that there was no cause for the dog to bark we have not explained why the dog did not bark. We may have explained why a nonbrute barking did not occur, but we have not explained why a brute, or unexplained, barking did not occur.