 Following the demanding conceptions of knowledge typical of his time that had been inspired by René Descartes’s (1596–1650) quest for certainty (see Descartes’s “method of doubt” and his “cogito” [Latin, for “I think”]), Schopenhauer maintained that if any explanation is to be genuine, then whatever is explained cannot be thought to have arisen by accident, but must be regarded as having been necessary. Schopenhauer’s investigation into the principle of sufficient reason can thus be alternatively characterized as an inquiry into the nature of the various kinds of necessary connection that can arise between different kinds of objects.