argues of something that if it exists that it is either contingent or necessary (Leibniz 236). This is indisputable. By "necessary," Leibniz means that the opposite involves a contradiction (Leibniz 236). Remember the claims of Kant and Russell. They hold that saying of something that it does not exist does not involve any contradiction. There is no dispute over this term. By "contingent," Leibniz means that the opposite is possible (Leibniz 236). For instance, it is possible that a chair exists and possible that a chair does not exist. That chairs exist is contingent. Again, there is an agreement on terms, and no equivocation.Leibniz, then, argues that there must be a reason sufficient to explain contingent things if there be such things (Leibniz 237). This is the principle of sufficient reason. This may not seem obvious at first glance, but it is evident with some thought. If there were no reason sufficient to explain a contingent thing, then either one means that its explanation is self-sufficient or that there is no reason sufficient to explain it. If the reason were self-sufficient, that would make it a necessary being, that is the opposite of which would involve a contradiction. If there were no knowable reason sufficient to explain it, then one cannot say that there is such a thing. Now, why does this follow? A contingent being has an opposite, meaning something that the contingent being is not, and opposites must be distinct from each other to be true opposites. If they are different, what is it that makes them different? The expression of the difference will take the form of an explanation. If there is no reason such that it will explain a contingent being, in what sense can it be said to be contingent as there has been established nothing that makes that being distinct from its opposite? In other words, it makes no sense to talk about the existence of a thing which cannot be at first understood, at least understood as distinct...
