 In his Fifth paper to Clarke, Leibniz argues for the PSR inductively. He says that there are many cases where a fact has a sufficient reason and no cases where fact is known not to have a sufficient reason. He then says that it is reasonable to assume that the PSR holds in all cases where we do not know that sufficient reason. Leibniz describes this as “the method of experimental philosophy, which proceeds a posteriori” (G VII 420; LC, L5.129).