"Our knowledge proceeds from two intellectual sources; the first is the capacity of receiving representations, (the receptivity of impressions,) the second is the faculty of knowing an object by these representations, (the spontaneity of conceptions.) By the former the object is given to us; by the latter, it is _thought_ in relation to this representation (as mere determination of the mind.) Intuition and conception constitute the elements of all our knowledge; so that neither conceptions without an intuition in some manner corresponding to them, nor an intuition without conceptions, can give knowledge. * * * * * "We call _sensibility_ the capacity (receptivity) of our mind to receive representations, so far as affected in any way whatever: on the contrary, the faculty of producing representations, or the _spontaneity_ of knowledge, is called _understanding_. Our nature is such that there can be no intuition not _sensible_, that is to say, which only comprehends the manner in which we are affected by objects. The _understanding_ is the faculty of _thinking_ the object of sensible intuition. Neither of these properties of the soul is preferable to the other. Without sensibility no object could be given to us; without the understanding none could be thought. Thoughts without contents are empty; intuitions without conceptions are blind. It is, then, just as necessary to make conceptions sensible,--that is, to give them an object in intuition, as to make intuitions intelligible, by subjecting them to conceptions. These two faculties or capacities cannot interchange their functions. The understanding can perceive nothing,[5] and the senses can think nothing. Knowledge results only from their union. Their attributes, therefore, ought not to be confounded; on the contrary, there is every reason to distinguish them, and to separate them with great care. We distinguish then the science of the laws of sensibility in general, that is to say, _Æsthetics_, from the science of the laws of the understanding in general, that is, from _Logic_."[6] [5] He speaks of intuitive perception, not of perception in general. [6] _Transcendental Logic._ Introduction. Mark well the meaning of this doctrine. Two facts are established; sensible intuition, and the conception of it; consequently the existence of two faculties, sensibility, and the understanding, is affirmed. To the first correspond sensible representations; to the latter conceptions. These two faculties, though different, are closely interlinked; and they are mutually necessary in order to produce cognitions. But how do they give each other that mutual aid they stand in need of?