Kant and the Principle of Sufficient Reason

For Leibniz, the principle of sufficient reason demands that for everything that is there must be a reason. Leibniz reasons that because there is no contingent thing that can be a sufficient reason for all other contingent things, we must look beyond the totality of existing things towards something which the totality can derive its existence from. This being that is the reason for the totality is God, and because God's essence is existence we have no need to demand a further reason for his existence.

Kant is considered to have advanced beyond Leibniz by showing that the sort of proof that Leibniz gives fails in what it promises. However, we should not be too quick to think that this rejection places Kant in complete opposition to Leibniz, since Kant still employs the principle of sufficient reason in the same manner that Leibniz does. We should consider just how different Kant's position is from Leibniz'.

Kant constrains the term 'existence' to apply only to objects of an actual experience, and since God is an object of even a possible experience, existence is improperly applied to him. Further, existence, as well as the other modalities of possibility and necessity, are not properties of things, but only represent the manner in which something is related to our mode of knowing it. In Kant's terminology, God isn't even possible; God is 'problematic', that is, we can think Him consistently, but have no way of knowing if he is possible or impossible (since He cannot be an object of possible experience). From this standpoint we easily see that Kant finds great problems in arguments for the existence of God. However, Kant does not count God out in this way, but realizes he must seek a different approach.

While showing that the ontological argument does not work, Kant still accepts the principle of sufficient reason as making a valid demand on us; the difference between Leibniz and Kant on this point is that Kant doesn't allow the demand from the principle to cause him to overstep the limits of his knowledge. However, Kant does show that we at least thinking beyond the boundary of theoretical reason, but just thinking beyond this boundary does not prove any existence.

However, what Kant calls 'practical reason' thinks intelligible being in terms of a necessary demand of the moral law. Under the heading of practical philosophy, Kant can begin to work towards the same position Leibniz maintained, however Kant will not attempt to maintain it as a known fact, but rather as a postulate of our practical manner of thinking. The best we can do is say 'God ought to be' as an expression of our constitution as knowers struggling against the demand our moral life places on us. I won't dwell on Kant's practical thought in relation to Leibniz here, but will only go into closer detail concerning Kant's use of the principle of sufficient reason for maintaining our capacity to think the intelligible.

Kant considers cause in the following way: whenever something happens, it presupposes something prior - a cause. (It is important to emphasize a happening.) If the cause is thought in terms of a happening, then it also must be thought as having a prior cause; if it is not thought in terms of a happening, then it is thought outside of the temporal order. Thus we can think a causal order stretching back indefinitely in the natural order, as well as spontaneous causes that are technically thought as supernatural. This shift from the natural order to the super-natural order is exactly how Leibniz argues for the existence of God. However, Kant still maintains that our capacity, and even need, to think these supernatural causes does not prove their existence, but a peculiarity of our form of cognition. In the realm of practical reason, Kant maintains that freedom, immortality and God are three postulates (roughly, assumptions); as postulates they are thought as really existing, however, we do not know them to exist even still.

Now, if Leibniz is to be similar to Kant, we would expect to find that there are moral grounds supporting Leibniz' determination of the existence of God, and not merely theoretical grounds as appears to be the case in his argumentation. It is plain to see that Leibniz' work is highly oriented towards living the best life possible, so there may be room to discover a reason to interpret Leibniz as operating from the very beginning in a practical mode, and so potentially being very close to Kant in the end. I hope to continue to look into this in further study.