Abstract: According to Principles of Sufficient Reason, every truth (in some relevant group) has an explanation. One of the most popular defenses of Principles of Sufficient Reason has been the presupposition of reason defense, which takes endorsement of the defended PSR to play a crucial role in our theory selection. According to recent presentations of this defense, our method of theory selection often depends on the assumption that, if a given proposition is true, then it has an explanation, and this will only be justified if we think this holds for all propositions in the relevant group. In this paper the author argues that this argument fails even when restricted to contingent propositions, and even if we grant that there is no non-arbitrary way to divide true propositions that have explanations from those that lack them. The author gives an alternate explanation of what justifies our selecting theories on the basis of explanatory features: the crucial role is not played by an endorsement of a PSR, but rather by our belief that, prima facie, we should prefer theories that exemplify explanatory power to greater degrees than their rivals.
Comment: The text covers many topics in a level proper for undergraduates: The principle of sufficient reason, the inductive argument, the problem of the Many, explanatory power, etc. Even if the reader doesn't identify with the view of the author, this article could serve as a good practice to build confidence with philosophical concepts that are crucial for metaphysics and philosophy of science.