Other works on Kant and on his Critical Philosophy attempt either to remove Kant's transcendental idealism from his system or to defend it as being essential to the Kantian enterprise. In Kant's Idealism, Professor Neujahr argues - he may be the first to do so - that there is no single doctrine that is Kant's transcendental idealism to either explain or explain away. In his Critique of Pure Reason, Kant claims to present a distinctive form of idealism he calls "transcendental" idealism and that he contrasts with the "empirical" idealism of his predecessors. Professor Neujahr argues that on the contrary there is no single form of idealism in Kant's system and no simple contrast between Kant's transcendental idealism and the idealist doctrines of his philosophical forebears. Neujahr finds (and clearly delineates) "strands of idealism" in Kant's philosophy. He argues that the source of these various forms of idealism is the conflicting demands of Kant's theories of perception (sensibility) and thought (understanding). How in fact a subject relates to an object finds no single unified explanation in the Critical Philosophy of Kant. Indeed, in spite of Kant's efforts to combine his various theories into a single theory of experience, his doctrines of perception and thought do not fit together. It is, Neujahr contends, this lack of fit that ultimately prevents there being any single transcendental version of idealism in Kant's system. This also helps explain why Kant's system is so difficult. Neujahr's critical review of that system in Kant's Idealism may be the "handle" needed to get hold of Kant's notoriously difficult but potentially very useful Critical Philosophy.