61. Experience teaches that this communication exists, conformably to a law of the human mind, and that to contend against the law is to struggle against a truth attested by consciousness: to attempt to destroy it would be a rash undertaking, a kind of mental suicide. For this reason, the school of which we have just spoken, accepts the facts, such as internal experience presents them, and endeavors to explain them by indicating the points where the sensible and intellectual orders may come into communication without being destroyed or confounded.
62. The school that admits the existence of the two orders, the sensible and the intellectual, and at the same time admits the possibility and the reality of their reciprocal communication and influence, has, for its fundamental principle, that the origin of all cognition is in the senses, these being the exciting causes of intellectual activity, and a kind of laborers who supply it with materials, which it then combines in the manner necessary to raise the scientifical structure.
63. Thus far, Kant and the scholastics agree; but here they separate at a point of the greatest importance, and the result is that they pass on to conflicting consequences. The scholastics believed that there were in the understanding true ideas having true objects, and that they might discuss them, independently of the sensible order, with perfect security. They even admitted the principle that there can be nothing in the understanding which was not previously in the senses; but pretended, nevertheless, that there really was something in the understanding, which might conduce to the knowledge of the truth of immaterial, as well as of material things in themselves. The ideas of the purely intellectual order originate in the senses as movers of the intellectual activity; but this activity, by means of abstraction and other operations, forms to itself ideas of its own, by whose aid it may go beyond the sensible order in its search for truth.
64. In their explanation of the purely intellectual order, metaphysicians, both scholastics and anti-scholastics agree, so far as there is question of giving a real objective value to ideas, and of making them a sure means of discovering truth independently of sensible phenomena. However much these schools disagree as to the origin of ideas, they agree in all that relates to their reality and value.
65. Kant, at the same time that he admits the principle of the scholastics, that all our cognitions come from the senses, and recognizes with them the necessity of acknowledging a purely intellectual order, a series of conceptions different from sensible intuition, maintains that these conceptions are not pure cognitions, but empty forms, which of themselves mean nothing, teach the mind nothing, and cannot, in the least, aid us to know the reality of things. These conceptions mean nothing unless filled, so to speak, with sensible intuitions. If these intuitions are wanting, they correspond to nothing, and can be of none but a purely logical use; that is to say, the understanding will think upon and combine them, without, indeed, falling into contradiction, but also without ever coming to any conclusion.
"That the understanding," Kant says, "can never make a transcendental, but only an empirical use, either of its a priori principles, or of its conceptions, is a principle which, if known with conviction, leads to the most important consequences. The transcendental use of a conception in any principle, consists in referring it to things, in general, and in themselves; whilst the empirical use is in referring the conception to phenomena alone, that is, to the objects of a possible experience, by which we may easily see that this latter use is the only one that can stand. To every conception is necessary, first of all, a logical form of a conception in general, of the thought: and secondly, the possibility of subjecting to it an object, to which it may refer; but without this object it wants all sense, it contains nothing, although it may involve the logical function necessary to form a conception by means of certain data. The object cannot be given to a conception except in intuition; and although pure intuition may be a priori possible before the object, it cannot, however, receive its object, and consequently its objective value, otherwise than by the empirical intuition of which it is the form. All conceptions and with them all principles, although they be possible a priori, do, notwithstanding, refer to empirical intuitions, that is, to data of possible experience. Without this they have no objective value; they are nothing but a mere play, whether of the imagination or of the understanding, with the respective representations of the one or the other faculty.
"That the same is the case with all the categories and principles formed from them, is apparent from this, that we cannot really define a single one of them; that is to say, we cannot render the possibility of their object intelligible without attending to the conditions of sensibility, and consequently to the form of the appearances; conditions to which these categories must be confined as to their sole objects. If this condition be taken away, all meaning, that is, all relation to the object is destroyed, and by no example can we be made to conceive what is the proper meaning of these conceptions.
"If no account be made of all the conditions of sensibility which denote them (he is speaking of the categories) as conceptions of a possible empirical use, if they be taken to be conceptions of things in general, and consequently, of transcendental use, nothing remains to be done, so far as they are concerned, but to preserve the logical functions in judgments, as the condition of the possibility of the things themselves, without being able to show in what case, their application and their object, and consequently they themselves, may, in the pure understanding, and without the intervention of sensibility, have a meaning and an objective value.
"It incontestably follows from what has been said, that pure conceptions of the understanding can never have a transcendental use, but only an empirical use; and that the principles of the pure understanding do not refer to the objects of the senses, except when the senses are in relation with the general conditions of a possible experience; but never to things in general, without relation to the way in which we may perceive them."8
66. Thus Kant destroys all metaphysical science, and, involved in its deplorable ruins, perish the most fundamental, most precious, and most sacred ideas of the human mind. According to him, transcendental analysis makes us see that the understanding can never pass the limits of sensibility, the only limits within which objects are given to us in intuition. These principles which were regarded as eternal pillars of the scientific edifice sink into empty forms, into words without meaning, so soon as they rise from the sphere of sensibility.
Ontology, with its transcendental doctrines, avails not in the eyes of the German philosopher to explain the nature and origin of things. "These principles," he says, "are simply principles of the exposition of phenomena; and the proud name of an ontology which pretends to give an a priori, synthetic cognition of things, in a systematic doctrine, for example, the principle of causality, ought to be replaced by the modest denomination of simple analysis of the pure understanding."
67. It would be hard to find a more noxious doctrine. What is left to the human mind when all means of rising from the sensible sphere are taken away? To what is our understanding reduced, if its most fundamental ideas, and its noblest principles can teach nothing concerning the nature of things? If the corporeal world is for us nothing but a collection of sensible phenomena, beyond which we can know nothing, our cognitions have nothing real, they are all purely subjective; the soul lives on illusions, and vanishes with its imaginary creations, to which there is nothing to correspond in reality. Space is but a subjective form; time is but a subjective form; pure ideas are empty conceptions, and all in us is subjective. We know nothing of objects, we are totally ignorant of what is; we know only what appears.