Leibniz defined the principle of sufficient reason as that which requires us to acknowledge that there is no fact or truth that lacks a sufficient reason why it should be so, and not otherwise. Our subjective epistemic nature is constituted to to assume that what is real is what is rational.
The PSR is not infertile. From it you can derive:
- That no two individuals can be exactly alike.
- That the physical world was not created at any point in time.
- That there is a (valid) answer to the question, Why is there something instead of nothing?
Following Kant, Schopenhauer limited the PSR and looked at its roots. He gets into how its basis is something about the subject:
Schopenhauer observed as an elementary condition, that to employ the principle of sufficient reason, we must think about something specific that stands in need of explanation. This indicated to him that at the root of our epistemological situation, we must assume the presence of a subject that thinks about some object to be explained. From this, he concluded that the general root of the principle of sufficient reason is the distinction between subject and object that must be presupposed as a condition for the very enterprise of looking for explanations (The Fourfold Root, § 16) and as a condition for knowledge in general.