As to Kant, the Vatican decree that the demonstrability of the existence of God by reason alone must be conceded on grounds of faith is prima facie exactly to reverse the priorities argued for in the Critique of Pure Reason, that it is on grounds of faith that such rational demonstrability must be denied. But the conflict is more complex and less direct than any such simple opposition of terms might suggest, if only because Kant argues at length and on purely philosophical grounds not only that all actual arguments for the existence of God fail of validity,2 but also that all possible arguments of speculative reason for the existence of God must in principle so fail.3 Moreover, when Kant says that he has 'found it necessary to deny knowledge in order to make room for faith',4 what he means by 'faith' is not the faith the council refers to, Christian faith as such, the divine gift of participation in God's own self-knowledge, but rather a rational moral faith, what he calls a 'postulate of practical reason'. In fact, what is at stake for Kant is the fundamental principle of his 'critical' philosophy, for which all forms of transcendent rational speculation must be denied in so far as to do so is required for the possibility of morality's proper freedom and rationality.
In summary, Kant's argument rests on the proposition that moral agents are free agents. But we cannot know, Kant argues, that we are free agents on the strength of any experience of freedom, for as natural beings our knowledge is limited by the constraints of 'experience' to appearances, and within the limits of appearance our actions are entirely subject to the necessities of causal law. Hence, within the limits of human experience freedom is excluded. Nonetheless, if we cannot 'experience'
2 Immanuel Kant, Critique of Pure Reason, B599-642, trans. Norman Kemp Smith, London: Macmillan, 1965, pp. 487-514.
3 Ibid., B659-70, pp. 525-531. 4 Ibid., Bxxx, Preface to 2nd edn, p. 29.
freedom, or establish it on the strength of any inference directly from sensory experience, we can 'think' - postulate - it, because we know that were we not free, then moral obligation would be impossible: for 'ought' implies 'can'. But moral obligation is possible, for the experience of it is a fact. Therefore, we are compelled to 'think' freedom as the condition of the possibility of moral experience, even if it can in no sense be an object of that, or any other, direct experience, for, as Kant says, 'we do not understand [freedom]; but we know it as the condition of the moral law which we do know'.5
If in one way freedom is thus a 'postulate of practical reason', so in another way are God and personal immortality. For practical reason can be sure of its hold on our minds and wills as categorical moral obligation only on condition that a moral order as such can be guaranteed. And that there is a moral order requires that virtue in its connection with human happiness is secured untroubled by the arbitrary vicissitudes of our secular condition (in which, de facto, they are frequently sundered). But an essential, and not merely contingent, connection between virtue and happiness can be guaranteed only by God and only if we survive beyond the arbitrary circumstances of our pre-mortem existence.6 However, none of these three, God, freedom or immortality, is given to us in any possible experience. All are postulates of practical reason and are in that sense 'faith' (Glaube) in that they are known not by any demonstrations of speculative reason from the world of appearance -'nature' - but only as the conditions of the possibility of morality.
Moreover, it is not just that, as 'postulates', they are not 'given in experience'. In that morality is possible, they could not be knowable within the limits of experience; and therefore the possibility of a demonstration of the existence of God must be ruled out for speculative reason in the name of practical reason. For if it were possible speculatively to demonstrate God's existence, or our freedom and immortality, 'from the consideration of created things' (as Vatican I puts it), then that freedom on which the possibility of morality depends would be cancelled thereby. For if causality in the world of appearances could be demonstrated to apply transcendently of the world - and that is what such a demonstration of God's existence would have to show - then, just as natural causality within
5 Immanuel Kant, Critique of Practical Reason, trans. and introd. Lewis W. Beck, New York: Liberal Arts Press, 1956, Preface, p. 4.
6 Kant is, of course, quite clear that happiness cannot be a proper motive of virtue, or of moral obligation generally. The connectedness of virtue with happiness must, however, be secured if moral obligation is to be construed as properly rational, that is to say, as having the character of an order. On all this see Critique of Practical Reason, II.II.v., pp. 128-36.
the world of 'appearances' rules out freedom as an object of experience, so a causality supposed to have application in the transcendent realm beyond appearances would have to rule out freedom there too, and with it the possibility of morality. In order, therefore, to make room for 'faith', that is for human freedom, immortality and God, and so for morality, the pretentious claim of speculative reason to a transcendent reach has to be denied it. And so Kant tells us that 'all attempts to employ reason in any merely speculative manner are altogether fruitless and by their very nature null and void, and . . . the principles of its employment in the study of nature do not lead to any theology whatever. Consequently, the only theology of reason which is possible is that which is based on moral laws'.7 Hence, the teaching of the Vatican Council that Christian faith entails the possibility of speculative rational proof of God stands in more or less straightforward conflict with Kant's view that moral faith, if not Christian faith as such, excludes just that possibility. At any rate, what the Vatican Council affirms is just that which Kant denies.
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