58. All philosophers agree in admitting the fact of sensibility; concerning it there can be no doubt; it is a phenomenon attested by consciousness in so palpable a manner, that not even skeptics could ever deny the subjective reality of the appearance, however much they called in question its objective reality. Idealists, when they deny the existence of bodies, do not deny their phenomenal appearance, their appearance to the mental eye under a sensible form. Sensibility then, and the phenomena it exhibits, have in all ages been primary data in ideological and psychological problems; there may be a discrepancy with respect to the nature and consequences of these data, but there can be none as to their existence.
59. The history of ideological science shows us two schools; one of which admits nothing but sensation, and explains all the affections and operations of the mind by the transformation of the senses; while the other admits primitive facts distinct from sensation; other faculties than that of feeling, and recognizes in the mind a line dividing the sensible from the intellectual order.
60. This latter school is divided into two others; one of which regards the sensible order as not only distinct, but also separate from the intellectual order, and in some sense at war with it; and it therefore maintains that the intellectual can receive nothing from the sensible order, except malign exhortations which either mislead it, or enervate its activity. Hence the system of innate ideas in all its purity; hence the metaphysics of an intellectual order entirely exempt from sensible impressions, metaphysics which, cultivated by eminent geniuses, has in modern times been professed by the author of the Investigation of Truth, with sublime exaggeration. The other ramification of the school also admits the pure intellectual order, but does not hold it to be contaminated by being brought into communication with sensible phenomena; on the contrary, it is rather inclined to believe that the problems of human intelligence, such as it exists in this life, cannot be resolved without fixing the mind upon the aforesaid communication.
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.