On the Principle of Sufficient Reason

The aim of this paper is to defend the ontological Principle of Sufficient Reason (PSR-O). I analyse various versions of this principle and various ways of justifying it. Then I attempt to challenge some counterexamples allegedly refuting a universal application of the PSR-O. There are standard and non-standard versions of the PSR-O. The PSR-Ostand can only be valid if there are no chains of contingent reasons and outcomes with first modules, i.e. all chains are actually infinite. However, there are serious arguments against this possibility. The necessary condition of the PSR-Onon-stand is the existence of a necessary substance: that substance would be a direct reason of certain contingent states of affairs obtaining in its domain, and those states of affairs would then be indirect reasons for all other contingent states of affairs and things. There are two advantages of the PSR-Onon-stand: a nomological unity of the world and explanatory simplicity