 (2) Idealism. During the nineteenth century, when pantheism was at its most popular, the dominant form was idealist. According to Absolute Idealism, as defended by such figures as Fichte, Schelling, Hegel, and many of the British Idealists, all that exists is a single spiritual entity, of which the physical world must be understood as a partial manifestation. The search for that which may be asserted without condition or qualification leads to the conclusion that all variety is the expression of an underlying unity, and that nothing can be real in the absence of mind or spirit. On some versions of this sort of doctrine the physical world starts to look more like an appearance of the ultimate spiritual (or possibly unknown) reality beneath. Hegel himself rejects this sort of doctrine —which he terms acosmism—and while it certainly amounts to a view that there exists nothing besides God, in view of its basic denial of the reality of the world we all experience it hardly seems like a kind of pantheism.