son； that in order to say that this world could be produced only by a God （according to the conception implied by this word） we should know this world as the most perfect whole possible； and for this purpose should also know all possible worlds （in order to be able to compare them with this）； in other words； we should be omniscient。 It is absolutely impossible； however； to know the existence of this Being from mere concepts； because every existential proposition； that is； every proposition that affirms the existence of a being of which I frame a concept； is a synthetic proposition； that is； one by which I go beyond that conception and affirm of it more than was thought in the conception itself； namely； that this concept in the understanding has an object corresponding to it outside the understanding； and this it is obviously impossible to elicit by any reasoning。 There remains； therefore； only one single process possible for reason to attain this knowledge； namely； to start from the supreme principle of its pure practical use （which in every case is directed simply to the existence of something as a consequence of reason） and thus determine its object。 Then its inevitable problem； namely； the necessary direction of the will to the summum bonum； discovers to us not only the necessity of assuming such a First Being in reference to the possibility of this good in the world； but； what is most remarkable； something which reason in its progress on the path of physical nature altogether failed to find； namely； an accurately defined conception of this First Being。 As we can know only a small part of this world； and can still less compare it with all possible worlds； we may indeed from its order； design； and greatness； infer a wise； good； powerful； etc。； Author of it； but not that He is all…wise； all…good； all…powerful； etc。 It may indeed very well be granted that we should be justified in supplying this inevitable defect by a legitimate and reasonable hypothesis； namely； that when wisdom； goodness； etc； are displayed in all the parts that offer themselves to our nearer knowledge； it is just the same in all the rest； and that it would therefore be reasonable to ascribe all possible perfections to the Author of the world； but these are not strict logical inferences in which we can pride ourselves on our insight； but only permitted conclusions in which we may be indulged and which require further recommendation before we can make use of them。 On the path of empirical inquiry then （physics）； the conception of God remains always a conception of the perfection of the First Being not accurately enough determined to be held adequate to the conception of Deity。 （With metaphysic in its transcendental part nothing whatever can be accomplished。） When I now try to test this conception by reference to the object of practical reason； I find that the moral principle admits as possible only the conception of an Author of the world possessed of the highest perfection。 He must be omniscient； in order to know my conduct up to the inmost root of my mental state in all possible cases and into all future time； omnipotent； in order to allot to it its fitting consequences； similarly He must be omnipresent； eternal； etc。 Thus the moral law； by means of the conception of the summum bonum as the object of a pure practical reason； determines the concept of the First Being as the Supreme Being； a thing which the physical （and in its higher development the metaphysical）； in other words； the whole speculative course of reason； was unable to effect。 The conception of God； then； is one that belongs originally not to physics； i。e。； to speculative reason； but to morals。 The same may be said of the other conceptions of reason of which we have treated above as postulates of it in its practical use。 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 making 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； freedom； and immortality； since I cannot prove these by my speculative reason； although neither can I refute them。 This duty is founded on something that is indeed quite independent of these suppositions and is of itself apodeictically certain； namely； the moral law； and so far it needs no further support by theoretical views as to the inner constitution of things； the secret final aim of the order of the world； or a presiding ruler thereof； in order to bind me in the most perfect manner to act in unconditional conformity to the law。 But the subjective effect of this law； namely； the mental disposition conformed to it and mad