Kant's mistaken formulation of the problem has had a greater or lesser influence on all subsequent students of the Theory of Knowledge. For Kant, the view that all objects which are given to us in experience are ideas in our minds is a consequence of his theory of the a priori. For nearly all his successors, it has become the first principle and starting-point of their epistemological systems. It is said that the first and most immediate truth is, simply and solely, the proposition that we know our own ideas. This has come to be a well-nigh universal conviction among philosophers. G. E. Schulze maintains in his Ænesidemus, as early as 1792, that all our cognitions are mere ideas and that we can never transcend our ideas. Schopenhauer puts forward, with all the philosophical pathos which distinguishes him, the view that the permanent achievement of Kant's philosophy is the thesis that "the world is my idea." To Eduard von Hartmann this thesis is so incontestable, that he addresses his treatise, Kritische Grundlegung des Transcendentalen Realismus, exclusively to readers who have achieved critical emancipation from the naïve identification of the world of perception with the thing-in-itself. He demands of them that they shall have made clear to themselves the absolute heterogeneity of the object of perception which through the act of representation has been given as a subjective and ideal content of consciousness, and of the thing-in-itself which is independent of the act of representation and of the form of consciousness and which exists in its own right. His readers are required to be thoroughly convinced that the whole of what is immediately given to us consists of ideas. [37] In his latest work on Theory of Knowledge, Hartmann does, indeed, attempt to give reasons for this view. What value should be attached to these reasons by an unprejudiced Theory of Knowledge will appear in the further course of our discussions. Otto Liebmann posits as the sacrosanct first principle of the Theory of Knowledge the proposition, "Consciousness cannot transcend itself." [38] Volkelt has called the proposition that the first and most immediate truth is the limitation of all our knowledge, in the first instance, to our own ideas exclusively, the positivistic principle of knowledge. He regards only those theories of knowledge as "in the fullest sense critical" which "place this principle, as the only fixed starting-point of philosophy, at the head of their discussions and then consistently think out its consequences." [39] Other philosophers place other propositions at the head of the Theory of Knowledge, e.g., the proposition that its real problem concerns the relation between Thought and Being, and the possibility of a mediation between them; [40] or that it concerns the way in which Being becomes an object of Consciousness; [41] and many others. Kirchmann starts from two epistemological axioms, "Whatever is perceived is," and, "Whatever