 With the notions of “possible thing”, “something”, and “nothing” firmly in hand, we can now explain the notion of reason (Grund or ratio) that Wolff includes in his definition of philosophy. Insofar as the subject matter of philosophy concerns the realm of all possible things, Wolff believes that the task of the philosopher is to provide “the manner and reason” of their possibility. Warrant for this claim is grounded in the idea that everything, whether possible or actual, has a “sufficient reason” for why it is rather than not. In §56 of his Ontologia, he writes: “By sufficient reason we understand that from which it is understood why something is [or can be]”. Unlike Leibniz who essentially restricts the notion of sufficient reason to “contingent truths of fact”, Wolff considers the notion to have a much broader scope of application to include the set of all possible objects and what Leibniz calls “necessary truths of reason”. The idea that everything has a sufficient reason is presented formally by Wolff as the principle of sufficient reason.