[Footnote 2:  The thing in itself denotes the object in so far as it can be thought by us, but not intuited, and consequently not determined by intuitions, i.e., cannot be known.  It is only through the schematism that the categories are limited to phenomena.  O. Liebmann (Kant und die Epigonen, p. 27, and passim) overlooks or ignores this when he says:  Kant here allows himself to “recognize an object emancipated from the forms of knowledge, therefore an irrational object, i.e., to represent something which is not representable—­wooden iron.”  The thing in itself is insensible, but not irrational, and the forms of intuition and forms of thought joined by Liebmann under the title forms of knowledge have in Kant a by no means equal rank.]

[Footnote 3:  A category by itself, freed from all conditions of intuition (e.g., the representation of a substance which is thought without permanence in time, or of a cause which should not act in time), can yield no definite concept of an object.]

Though the concepts of the understanding possess a cognitive value in the sphere of phenomena alone, the hope still remains of gaining an entrance into the suprasensible sphere through the concepts of reason.  It is indubitable that our spirit is conscious of a far higher need than that for the mere connection of phenomena into experience; it is that which cannot be experienced, the Ideas God, freedom, and immortality, which form the real end of its inquiry.  Can this need be satisfied, and how?  Can this end be attained, and reality be given to the Ideas?  This is the third question of the Critique of Reason.

%(c) The Reason’s Ideas of the Unconditioned (Transcendental Dialectic).%—­“All our knowledge begins with the senses, proceeds thence to the understanding, and ends with reason.”  The understanding is the faculty of rules, reason the faculty of principles.  The categories of the understanding are necessary concepts which make experience possible, and which, therefore, can always be given in experience; the Ideas of reason are necessary concepts to which no corresponding object can be given.  Each of the Ideas gives expression to an unconditioned.  How does the concept of the unconditioned arise, and what service does it perform for knowledge?

As perceptions are connected by the categories in the unity of the understanding, and thus are elevated into experience, so the manifold knowledge of experience needs a higher unity, the unity of reason, in order to form a connected system.  This is supplied to it by the Ideas—­which, consequently, do not relate directly to the objects of intuition, but only to the understanding and its judgments—­in order, through the concept of the unconditioned, to give completion to the knowledge of the understanding, which always moves in the sphere of the conditioned, i.e., to give it the greatest possible unity together with the greatest possible extension.