It may be sufficient in this place to define theoretical knowledge or cognition as knowledge of that which is, and practical knowledge as knowledge of that which ought to be.In this view, the theoretical employment of reason is that by which I cognize a priori (as necessary) that something is, while the practical is that by which Icognize a priori what ought to happen.Now, if it is an indubitably certain, though at the same time an entirely conditioned truth, that something is, or ought to happen, either a certain determinate condition of this truth is absolutely necessary, or such a condition may be arbitrarily presupposed.In the former case the condition is postulated (per thesin), in the latter supposed (per hypothesin).
There are certain practical laws- those of morality- which are absolutely necessary.Now, if these laws necessarily presuppose the existence of some being, as the condition of the possibility of their obligatory power, this being must be postulated, because the conditioned, from which we reason to this determinate condition, is itself cognized a priori as absolutely necessary.We shall at some future time show that the moral laws not merely presuppose the existence of a Supreme Being, but also, as themselves absolutely necessary in a different relation, demand or postulate it- although only from a practical point of view.The discussion of this argument we postpone for the present.
When the question relates merely to that which is, not to that which ought to be, the conditioned which is presented in experience is always cogitated as contingent.For this reason its condition cannot be regarded as absolutely necessary, but merely as relatively necessary, or rather as needful; the condition is in itself and a priori a mere arbitrary presupposition in aid of the cognition, by reason, of the conditioned.If, then, we are to possess a theoretical cognition of the absolute necessity of a thing, we cannot attain to this cognition otherwise than a priori by means of conceptions; while it is impossible in this way to cognize the existence of a cause which bears any relation to an existence given in experience.
Theoretical cognition is speculative when it relates to an object or certain conceptions of an object which is not given and cannot be discovered by means of experience.It is opposed to the cognition of nature, which concerns only those objects or predicates which can be presented in a possible experience.
The principle that everything which happens (the empirically contingent) must have a cause, is a principle of the cognition of nature, but not of speculative cognition.For, if we change it into an abstract principle, and deprive it of its reference to experience and the empirical, we shall find that it cannot with justice be regarded any longer as a synthetical proposition, and that it is impossible to discover any mode of transition from that which exists to something entirely different- termed cause.Nay, more, the conception of a cause likewise that of the contingent- loses, in this speculative mode of employing it, all significance, for its objective reality and meaning are comprehensible from experience alone.
When from the existence of the universe and the things in it the existence of a cause of the universe is inferred, reason is proceeding not in the natural, but in the speculative method.For the principle of the former enounces, not that things themselves or substances, but only that which happens or their states- as empirically contingent, have a cause: the assertion that the existence of substance itself is contingent is not justified by experience, it is the assertion of a reason employing its principles in a speculative manner.If, again, I infer from the form of the universe, from the way in which all things are connected and act and react upon each other, the existence of a cause entirely distinct from the universe- this would again be a judgement of purely speculative reason; because the object in this case- the cause- can never be an object of possible experience.In both these cases the principle of causality, which is valid only in the field of experience- useless and even meaningless beyond this region, would be diverted from its proper destination.