Leibniz, Kant and the Principle of Sufficient Reason: Part I

   Leibniz and Kant share a great deal in common, and we can come to appreciate both thinkers more through getting a sense of how their thoughts meet.  One point of Kant's thought opened up when related to Leibniz's concerns the principle of sufficient reason which states that there is nothing without a reason.  I will briefly cast a glance at what seems most different about Kant and Leibniz in relation to this principle, and then describe how it is that these differences are different so that they can once again fall into a relationship of sameness.

   Through the principle of sufficient reason Leibniz understands a demand placed on us to provide grounds for every finite truth.  For example, whatever happens depends on something before, and this gives us an infinite series.  But what is the sufficient reason for the existence of this entire causal series?  The being which stands beyond the series of causes as its ground is God, and, being infinite, God requires no further ground.  We recognize this as the cosmological argument, and may remember that Kant found it to be insufficient.  This insufficiency of the cosmological argument is just one instance where Kant found our reasoning goes astray, but this insufficiency is symptomatic of reason's whole functioning.  This signals a marked difference in the attitude Kant has towards the role of the principle of sufficient reason.

   The very first sentence of the Critique of Pure Reason, which I quote on this blog frequently, reads:
"Human reason has this peculiar fate that in one species of its knowledge it is burdened by questions which, as prescribed by the very nature of reason itself, it is not able to ignore, but which, as transcending all its powers, it is also not able to answer."

These "questions prescribed by the very nature of reason" that transcend reason pertain to what Kant describes as the ideas: soul, World and God.  Among other descriptions, Kant calls reason the faculty of ideas.  As the faculty of ideas, it pursues the unconditioned of the different series of relations.  This is much in the same spirit of Leibniz, as we can easily see that what reason demands of us in the questions it prescribes is the same as the demands of the principle of sufficient reason.  However, for Kant, while a sufficient reason is demanded, human cognition is insufficient to the task - at least in its theoretical employment, that is, when it concerns knowledge of what exists.

   Because Leibniz confidently proceeds with the great principle of sufficient reason to God, and Kant does not, it seems to us that this is a great point of difference between these to great thinkers.    However, we may not understand this difference.  We can align Kant with Leibniz by pointing out that even while Kant says that we cannot attain to a knowledge of the unconditioned, reason still has this idea which pushes us towards such completeness.  For Kant, we do posit God as that which grounds coherence, even if it is merely as an idea.  Further, Kant's denial of our knowing God's existence ultimately amounts to the inability to be given any (empirical) intuition of Him.  Leibniz would also agree that we do not sense God, and so Leibniz would agree that if knowledge of existence requires a possible intuition, then we cannot possibly come into this relation to God.  For Kant, God is part of our nature, for Leibniz, God is something we satisfy ourselves about with a proof.

   Leibniz takes the employment - the use - of the principle of sufficient reason in relation to all the finite world demands that we must assent to the existence of God (I must note again that existence does not mean the same thing here that it means for Kant).  Kant, on the other hand, does not speak of the principle of sufficient reason when discussing the ideas, but it is clear that he sees reason as the operation of that principle - not as a piece of equipment which we employ for use relative to this or that truth, but concerning the demand our own nature puts on us a priori.  While Kant denies that we can know the existence of God, God is still a necessary idea of reason governing the coherence of all knowledge.  This is to say, that Leibniz's argument is not wrong, but it is an argument which need not, perhaps should not, be given: our very nature is already entangled with the form of this argument.  But, what is the problem of giving the argument?
   (Heidegger noted that Kant took the scandal of philosophy to be that no proof of the external world has been given, and, maybe, Heidegger thought he improved Kant by saying that the real scandal is that we tried to prove the external world at all.  Perhaps we can see now that Kant did not need any assistance from Heidegger, though we can appreciate his clarification.)  

   Kant does not argue for God's existence, but rather shows how God is posited by our very nature — by reason.  Everything we argue about – that we speak about – is in conformity with our way of thinking, and so has the character of an object in general.  This means that it depends upon the possible application of the categories - it depends upon the temporal.  If we are to give an argument for God's existence (or the existence of the external world) we begin to treat God under the categories, and bring him implicitly into the scheme of the temporal as if he were another thing among others which would required something to cohere it with all other beings - that is to say, the sort of God we argue for is restricted in advance to require an even higher God (just as Parmenides points out for Socrates the problem of the regress in forms).   I hope to deal with this more completely in another place.

   For Kant, God must remain 'problematic', which is to say, indeterminate whether it is possible or impossible.  God must remain this way at least for theoretical reason, which concerns existence, but as a posit that guides our activity - as a maxim - God has a practical reality for us.  Kant's conception of Practical Reason is another key for coming to understand how this difference between Leibniz and Kant, and perhaps will guide us to see how Leibniz is justified in arguing for the existence of God without the result of him being a member of an even high order series.

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.