All pure a priori cognition forms, therefore, in view of the peculiar faculty which originates it, a peculiar and distinct unity;and metaphysic is the term applied to the philosophy which attempts to represent that cognition in this systematic unity.The speculative part of metaphysic, which has especially appropriated this appellation- that which we have called the metaphysic of nature- and which considers everything, as it is (not as it ought to be), by means of a priori conceptions, is divided in the following manner.
Metaphysic, in the more limited acceptation of the term, consists of two parts- transcendental philosophy and the physiology of pure reason.The former presents the system of all the conceptions and principles belonging to the understanding and the reason, and which relate to objects in general, but not to any particular given objects (Ontologia); the latter has nature for its subject-matter, that is, the sum of given objects- whether given to the senses, or, if we will, to some other kind of intuition- and is accordingly physiology, although only rationalis.But the use of the faculty of reason in this rational mode of regarding nature is either physical or hyperphysical, or, more properly speaking, immanent or transcendent.
The former relates to nature, in so far as our knowledge regarding it may be applied in experience (in concreto); the latter to that connection of the objects of experience, which transcends all experience.Transcendent physiology has, again, an internal and an external connection with its object, both, however, transcending possible experience; the former is the physiology of nature as a whole, or transcendental cognition of the world, the latter of the connection of the whole of nature with a being above nature, or transcendental cognition of God.
Immanent physiology, on the contrary, considers nature as the sum of all sensuous objects, consequently, as it is presented to us- but still according to a priori conditions, for it is under these alone that nature can be presented to our minds at all.The objects of immanent physiology are of two kinds: 1.Those of the external senses, or corporeal nature; 2.The object of the internal sense, the soul, or, in accordance with our fundamental conceptions of it, thinking nature.The metaphysics of corporeal nature is called physics; but, as it must contain only the principles of an a priori cognition of nature, we must term it rational physics.The metaphysics of thinking nature is called psychology, and for the same reason is to be regarded as merely the rational cognition of the soul.
Thus the whole system of metaphysics consists of four principal parts: 1.Ontology; 2.Rational Physiology; 3.Rational cosmology; and 4.Rational theology.The second part- that of the rational doctrine of nature- may be subdivided into two, physica rationalis* and psychologia rationalis.
*It must not be supposed that I mean by this appellation what is generally called physica general is, and which is rather mathematics than a philosophy of nature.For the metaphysic of nature is completely different from mathematics, nor is it so rich in results, although it is of great importance as a critical test of the application of pure understanding-cognition to nature.For want of its guidance, even mathematicians, adopting certain common notions-which are, in fact, metaphysical- have unconsciously crowded their theories of nature with hypotheses, the fallacy of which becomes evident upon the application of the principles of this metaphysic, without detriment, however, to the employment of mathematics in this sphere of cognition.
The fundamental idea of a philosophy of pure reason of necessity dictates this division; it is, therefore, architectonical- in accordance with the highest aims of reason, and not merely technical, or according to certain accidentally-observed similarities existing between the different parts of the whole science.For this reason, also, is the division immutable and of legislative authority.But the reader may observe in it a few points to which he ought to demur, and which may weaken his conviction of its truth and legitimacy.
In the first place, how can I desire an a priori cognition or metaphysic of objects, in so far as they are given a posteriori? and how is it possible to cognize the nature of things according to a priori principles, and to attain to a rational physiology? The answer is this.We take from experience nothing more than is requisite to present us with an object (in general) of the external or of the internal sense; in the former case, by the mere conception of matter (impenetrable and inanimate extension), in the latter, by the conception of a thinking being- given in the internal empirical representation, I think.As to the rest, we must not employ in our metaphysic of these objects any empirical principles (which add to the content of our conceptions by means of experience), for the purpose of forming by their help any judgements respecting these objects.