Central to Hegel's conception of knowledge and mind (and therefore also of reality) was the notion of identity in difference, that is that mind externalizes itself in various forms and objects that stand outside of it or opposed to it, and that, through recognizing itself in them, is "with itself" in these external manifestations, so that they are at one and the same time mind and other-than-mind. This notion of identity in difference, which is intimately bound up with his conception of contradiction and negativity, is a principal feature differentiating Hegel's thought from that of other philosophers.