According to Kant metaphysics is the “occupation of reason with itself”. In more concrete terms, it is the mind making logical connections between a priori concepts and coming to an objective truth thereby, without reference to experience. The question posed by him in the Prolegomena is whether such an objective truth is at all possible. The conclusion derived in the end is that there is indeed such an objective truth, which is effected through pure reason. But equally important in the assertion is that such metaphysics is beyond human understanding.
The title “Prolegomena to Any Future Metaphysics” suggests that Kant does indeed anticipate an irrefutable metaphysics to be in the grasp of men in the future, but he never makes such a claim in the text itself. The thing that Kant aimed for was clarity in the field of metaphysical endeavor, and this is the ‘future metaphysics’. ‘Future’ can be interpreted in two ways here. First in the sense already suggested, so that metaphysical thinking is founded on a scientific basis, in which the terms and strategies it employs are well defined. But it can also be hinting at transcendental possibility, that by which all contradictions are resolved through “pure reason”.
Scientific clarity is the aim, and thus Kant justifies the labor involved in Critique Of Pure Reason (1781), of which the Prolegomena was a sequel meant to make more accessible. He is at pains to point out that there is a moral obligation involved here. People cannot surrender themselves to unreason, because reason is the very make-up of the human, so postulates Kant. The suggestion that reason be abandoned was made by David Hume, who had spelt out a comprehensive theory of empirical skepticism.
All our knowledge is through sense perceptions, therefore are entirely subjective, and cannot be tied into an absolute whole through the application of reason. It is merely by the means of custom that we acquire a coherent worldview, he maintained. Kant saw this as a capitulation to unreason. It was not just Hume’s personal viewpoint that mattered. It was indeed a wider crisis in metaphysics that he was addressing.
When Newton’s physics could not be subsumed under any metaphysics, this engendered an intellectual confusion, and Hume’s solution was that metaphysics be abandoned as impossible. Kant enjoined that it is impossible to abandon metaphysics, for man reasons by necessity. Instead of finality we must aim for metaphysical clarity, and this is absolutely contingent upon us, indeed a moral obligation. He made what seem to be boastful claims about the crucial importance of the Critique in the history of metaphysics, but a closer examination will show that it is not from conceit, but rather from moral outrage.
The true nature of metaphysics is laid out with scientific clarity in the Critique and the Prolegomena, and this is the essence that Kant wants to convey, not the final outcome. He takes Hume to task in the very opening of the Critique: Although all our knowledge begins with experience, it does not follow that it arises entirely from experience. For it is quite possible that our empirical knowledge is a compound of that which we receive through impressions and that which our own faculty of knowing (incited by impressions) supplies from itself.
When considering sensual perception he first makes the distinction between a priori and a posteriori, the first suggesting an innate facility of the mind, and the second is a facility borne after the event. The second distinction is between analytical and synthetic propositions. In an analytic proposition the predicate is contained within the subject, such as “the flamingo is a bird”. In a synthetic proposition the predicate adds something new to the subject, such as “the flamingo is pink”. The pinkness is not in the definition of flamingo, but rather has to be got from observation, and therefore it is also a posteriori.
Synthetic a posteriori propositions are employed in the field of natural science. On the other hand all mathematical truths are innate, i.e. we ascertain their truth before sensory perception. They are also synthetic: when we say “3+4=7”, then ‘7’ is a new concept, not contained in either ‘3’ of ‘4’. Mathematics holds the key to metaphysics, according to Kant. It demonstrates that synthetic a priori propositions are possible, which is contrary to normal expectation. We feel that whatever is innate is necessarily analytical. We are what we are, separated from the objective natural world beyond us. Against this instinctive point of view, Kant contended that we are not passive observers of an external world separated from us, but that with our innate faculties we “synthesize” our own subjective reality.
The first stage of this synthesis is when we intuit objects in our perception. “Things in themselves” can never appear to us; we only have subjective sensory data to work with. It is a meaningless jumble of light, sound, touch, taste and smell, but then our faculty of sensibility intervenes and creates order out of this chaos. This faculty is synthetic a priori, and makes use of pure intuitions. Space is one such pure intuition. Newton had maintained that space is an external, absolute and inviolable reality. Kant counters that, no, space is pure intuition. Time is another such.
Through the faculties of sensibility we come to make a judgment of perception. Thus far it is an entirely subjective viewpoint, with no objective framework to relate to that would link our views with those of others. This is the function of our judgment of experience. It too is synthetic a priori, and links the objects of perception into a rational order that facilitates understanding. This is done through pure concepts of understanding, and causation is one of them. Through this faculty we know that one event is cause to another, and thus wise we have come across Hume’s impasse, where he could find no rational construct that could link a effect to a cause when confined to empirical sense data. “Cause and effect” is thus a concept of human understanding. Such understanding is composed of components that are a priori and synthetic, and it is meant to make the world intelligible to us.
Just because the world is made intelligible, it does not imply that we do not meet contradiction. When we think we do so discursively, i.e. we think by making propositions in terms of subjects and predicates. But each subject we introduce is the predicate of another subject in an infinite chain. Because the absolute subject is beyond our grasp, discursive reason naturally leads to fallacies. In fact each truthful proposition will be found to have an equally valid refutation, which together are described as pairs of antimonies. Kant cites four cosmological antimonies, one of which places infinite space against a limited one. He goes on to show that there is no contradiction in essence. As originating in the judgment of perception space does indeed have a beginning. But as regards human understanding space is necessarily infinite. The conflict arises from metaphysics failing to distinguish the noumenal (thing in itself) from the phenomenal (as appears to human understanding).
Thus far does metaphysics gain clarity, but not finality. The human mind cannot help ponder on the questions of metaphysics, but it must come to terms with the fact that it is ‘bounded’. Human understanding is meant to make the outer world intelligible, and thus proves inadequate when the focus is redirected to the inner essence of the mind, which is the object that metaphysics must study. But the overriding lesson of metaphysics is that pure reason subsumes all. One must not despair of human reason, for one must know that it originates in pure reason and is overcome by it in the end.
Subservience to pure reason is indeed a moral obligation. Other than clarity in metaphysics, which is not suitable for all, Kant advanced his categorical imperative: “I ought never to act except in such a way that I could also will that my maxim should become a universal law.” We cannot help noticing that this is only a rewording of the golden rule of Christianity: “Do unto others as you would they should do unto you.” Thus through clarity in metaphysics Kant can be said to have arrived at religious doctrine too.
Hume, David. An Enquiry Concerning Human Understanding. Ed. Eric Steinberg. Boston: Hackett Publishing, 1993.
Jeffrey, David L. A Dictionary of Biblical Tradition in English Literature. Grand Rapids, MI: Wm. B. Eerdmans Publishing, 1992.
Kant, Immanuel. Critique of Pure Reason. Trans. Werner S. Pluhar. Ed. Eric Watkins. Boston: Hackett Publishing Company, 1999.
Kant, Immanuel. Groundwork of the Metaphysics of Morals. Ed. Mary Gregor. Cambridge: Cambridge University Press, 1998.
Kant, Immanuel. Kant’s Prolegomena to Any Future Metaphysics. Whitefish, MT: Kessinger Publishing, 2005.
 Immanuel Kant, Kant’s Prolegomena to Any Future Metaphysics, Whitefish, MT: Kessinger Publishing, 2005, p. 92.
 David Hume, An Enquiry Concerning Human Understanding, Ed. Eric Steinberg, Boston: Hackett Publishing, 1993, p. 29.
 Immanuel Kant, Critique of Pure Reason. Trans. Werner S. Pluhar, Ed. Eric Watkins, Boston: Hackett Publishing Company, 1999, p. 1.
 Hume, Enquiry, p. 49.
 Immanuel Kant, Groundwork of the Metaphysics of Morals, Ed. Mary Gregor, Cambridge: Cambridge University Press, 1998, p. 16.
 David L. Jeffrey, A Dictionary of Biblical Tradition in English Literature, Grand Rapids, MI: Wm. B. Eerdmans Publishing, 1992, p. 314.