99. In order to prove the sterility of all conception beyond sensible intuition, Kant adduces one reason, which is, that we cannot define the categories and the principles which flow from them without referring to the objects of sensibility. This is no proof at all; for, in the first place, the impossibility of a definition does not always arise from the fact that the conception to be defined is empty; but it very frequently results from the conception being simple, and consequently not susceptible of a division into parts that may be expressed by words. How will he define the idea of _being_? No matter how he attempts to define it, the thing to be defined will enter into the definition: the words, thing, reality, existence, all signify _being_. It is very natural, since sensible intuition is the basis of our relations with the external world, and consequently with our fellow-men, that when we purpose to express any relation whatever, we should call to our aid sensible applications; but we are not thence to infer that there is not in our mind, independently of them, a real truth contained in the conception which we wish to explain. 100. This capacity of knowing objects under general ideas, is a characteristic property of our mind, and we cannot, in our inability to penetrate to the essence of things, think without this indispensable auxiliary. In the ordinary course of human affairs, it often happens that we need to know the existence of a thing and of some of its attributes, but do not require a perfect knowledge of it. In such cases, general ideas, aided by some data of experience, put us in mediate communication with the object not presented to our intuition. But why cannot the same thing be verified with respect to non-sensible beings, which alone are the object of intellectual intuitions? I know not what exception can be taken to these observations, founded as they are upon observation of internal phenomena, and confirmed by common sense. CHAPTER XVI. VALUE OF PRINCIPLES, INDEPENDENTLY OF SENSIBLE INTUITION. 101. The principle of contradiction, indispensable condition of all certainty, of all truth, and without which the external world, and intelligence itself, would become a chaos, offers us a good example of the intrinsic value of purely intellectual conceptions independent of sensible intuition.