In the history of Grecian philosophy we find no distinct traces of a pure rational theology earlier than Anaxagoras; but this is not because the older philosophers had not intelligence or penetration enough to raise themselves to it by the path of speculation, at least with the aid of a thoroughly reasonable hypothesis.What could have been easier, what more natural, than the thought which of itself occurs to everyone, to assume instead of several causes of the world, instead of an indeterminate degree of perfection, a single rational cause having all perfection? But the evils in the world seemed to them to be much too serious objections to allow them to feel themselves justified in such a hypothesis.They showed intelligence and penetration then in this very point, that they did not allow themselves to adopt it, but on the contrary looked about amongst natural causes to see if they could not find in them the qualities and power required for a First Being.But when this acute people had advanced so far in their investigations of nature as to treat even moral questions philosophically, on which other nations had never done anything but talk, then first they found a new and practical want, which did not fail to give definiteness to their conception of the First Being: and in this the speculative reason played the part of spectator, or at best had the merit of embellishing a conception that had not grown on its own ground, and of applying a series of confirmations from the study of nature now brought forward for the first time, not indeed to strengthen the authority of this conception (which was already established), but rather to make a show with a supposed discovery of theoretical reason.
From these remarks, the reader of the Critique of Pure Speculative Reason will be thoroughly convinced how highly necessary that laborious deduction of the categories was, and how fruitful for theology and morals.For if, on the one hand, we place them in pure understanding, it is by this deduction alone that we can be prevented from regarding them, with Plato, as innate, and founding on them extravagant pretensions to theories of the supersensible, to which we can see no end, and by which we should make theology a magic lantern of chimeras; on the other hand, if we regard them as acquired, this deduction saves us from restricting, with Epicurus, all and every use of them, even for practical purposes, to the objects and motives of the senses.But now that the Critique has shown by that deduction, first, that they are not of empirical origin, but have their seat and source a priori in the pure understanding; secondly, that as they refer to objects in general independently of the intuition of them, hence, although they cannot effect theoretical knowledge, except in application to empirical objects, yet when applied to an object given by pure practical reason they enable us to conceive the supersensible definitely, only so far, however, as it is defined by such predicates as are necessarily connected with the pure practical purpose given a priori and with its possibility.The speculative restriction of pure reason and its practical extension bring it into that relation of equality in which reason in general can be employed suitably to its end, and this example proves better than any other that the path to wisdom, if it is to be made sure and not to be impassable or misleading, must with us men inevitably pass through science; but it is not till this is complete that we can be convinced that it leads to this goal.
VIII.Of Belief from a Requirement of Pure Reason.
A want or requirement of pure reason in its speculative use leads only to a hypothesis; that of pure practical reason to a postulate;for in the former case I ascend from the result as high as I please in the series of causes, not in order to give objective reality to the result (e.g., the causal connection of things and changes in the world), but in order thoroughly to satisfy my inquiring reason in respect of it.Thus I see before me order and design in nature, and need not resort to speculation to assure myself of their reality, but to explain them I have to presuppose a Deity as their cause; and then since the inference from an effect to a definite cause is always uncertain and doubtful, especially to a cause so precise and so perfectly defined as we have to conceive in God, hence the highest degree of certainty to which this pre-supposition can be brought is that it is the most rational opinion for us men.* On the other hand, a requirement of pure practical reason is based on a duty, that of ****** something (the summum bonum) the object of my will so as to promote it with all my powers; in which case I must suppose its possibility and, consequently, also the conditions necessary thereto, namely, God, *******, and immortality; since I cannot prove these by my speculative reason, although neither can I refute them.