The estimate of our rational cognition a priori at which we arrive is that it has only to do with phenomena, and that things in themselves, while possessing a real existence, lie beyond its sphere.Here we are enabled to put the justice of this estimate to the test.For that which of necessity impels us to transcend the limits of experience and of all phenomena is the unconditioned, which reason absolutely requires in things as they are in themselves, in order to complete the series of conditions.Now, if it appears that when, on the one hand, we assume that our cognition conforms to its objects as things in themselves, the unconditioned cannot be thought without contradiction, and that when, on the other hand, we assume that our representation of things as they are given to us, does not conform to these things as they are in themselves, but that these objects, as phenomena, conform to our mode of representation, the contradiction disappears: we shall then be convinced of the truth of that which we began by assuming for the sake of experiment; we may look upon it as established that the unconditioned does not lie in things as we know them, or as they are given to us, but in things as they are in themselves, beyond the range of our cognition.**This experiment of pure reason has a great similarity to that of the chemists, which they term the experiment of reduction, or, more usually, the synthetic process.The analysis of the metaphysician separates pure cognition a priori into two heterogeneous elements, viz., the cognition of things as phenomena, and of things in themselves.Dialectic combines these again into harmony with the necessary rational idea of the unconditioned, and finds that this harmony never results except through the above distinction, which is, therefore, concluded to be just.
But, after we have thus denied the power of speculative reason to make any progress in the sphere of the supersensible, it still remains for our consideration whether data do not exist in practical cognition which may enable us to determine the transcendent conception of the unconditioned, to rise beyond the limits of all possible experience from a practical point of view, and thus to satisfy the great ends of metaphysics.Speculative reason has thus, at least, made room for such an extension of our knowledge: and, if it must leave this space vacant, still it does not rob us of the liberty to fill it up, if we can, by means of practical data- nay, it even challenges us to make the attempt.**So the central laws of the movements of the heavenly bodies established the truth of that which Copernicus, first, assumed only as a hypothesis, and, at the same time, brought to light that invisible force (Newtonian attraction) which holds the universe together.The latter would have remained forever undiscovered, if Copernicus had not ventured on the experiment- contrary to the senses but still just-of looking for the observed movements not in the heavenly bodies, but in the spectator.In this Preface I treat the new metaphysical method as a hypothesis with the view of rendering apparent the first attempts at such a change of method, which are always hypothetical.
But in the Critique itself it will be demonstrated, not hypothetically, but apodeictically, from the nature of our representations of space and time.and from the elementary conceptions of the understanding.
This attempt to introduce a complete revolution in the procedure of metaphysics, after the example of the geometricians and natural philosophers, constitutes the aim of the Critique of Pure Speculative Reason.It is a treatise on the method to be followed, not a system of the science itself.But, at the same time, it marks out and defines both the external boundaries and the internal structure of this science.For pure speculative reason has this peculiarity, that, in choosing the various objects of thought, it is able to define the limits of its own faculties, and even to give a complete enumeration of the possible modes of proposing problems to itself, and thus to sketch out the entire system of metaphysics.For, on the one hand, in cognition a priori, nothing must be attributed to the objects but what the thinking subject derives from itself; and, on the other hand, reason is, in regard to the principles of cognition, a perfectly distinct, independent unity, in which, as in an organized body, every member exists for the sake of the others, and all for the sake of each, so that no principle can be viewed, with safety, in one relationship, unless it is, at the same time, viewed in relation to the total use of pure reason.Hence, too, metaphysics has this singular advantage- an advantage which falls to the lot of no other science which has to do with objects- that, if once it is conducted into the sure path of science, by means of this criticism, it can then take in the whole sphere of its cognitions, and can thus complete its work, and leave it for the use of posterity, as a capital which can never receive fresh accessions.For metaphysics has to deal only with principles and with the limitations of its own employment as determined by these principles.To this perfection it is, therefore, bound, as the fundamental science, to attain, and to it the maxim may justly be applied:
