Experience cannot be adequate to the transcendental idea of a necessary and self-sufficient being, "so overwhelmingly great, so high above everything empirical" (A621/B649). The supreme being cannot be an object of experience, but if apart from experience, it is unreachable, given that the laws of experience apply only to its objects. To be sure, the world presents us with incredible marvels, but these only leave us speechless. Nonetheless, the proof is "the oldest, the clearest, and the most accordant with the study of nature" (A623/B651). It also guides us in seeking purpose in the world, and is reinforced when we find it. But we cannot grant the argument certainty, only "a belief adequate to quieten our doubts, though not to command unconditional submission" (A625/B653). Ultimately, certainty could only be found through the ontological argument, if it were cogent.
The argument iself has these features: (1) clear signs of order in a huge and varied universe, (2) the source of the order not being attributable to the things themselves, (3) the existence of an intelligent cause, (4) the unity of that cause as necessary for the deep interconnection in the world. The analogy to human artifice must not be taken too literally, but it is the only way we can proceed. "Reason could never be justified in abandoning the causality which it knows for gounds of explanation which are obscure, of which it does not have any knowledge, and which are incapable of proof" (A626/B654). Kant noted that this argument could at most show the existence of an architect of the world, not that of a creator.Further, the argument could not show the existence of a perfect being, but only one that is great to an indeterminate degree. Only an a priori argument such as the cosmological could do this. So the design argument depends on the cosmological, which itself is only the ontological argument in disguised.
The Regulative Use of Reason
Kant believed that the design argument, though in a sense furthest from establishing its conclusion, is the most compelling of the three arguments for the existence of God. For it exhibits the idea of God in its most concrete and useful form. It is useful in that the idea introduces systematic unity into the world of experience as we find it, rather than into the world conceived in general. This unity in turn serves as a guide for our investigation of it. "We declare . . . that the things of the world must be viewed as if they received their existence from a highest intelligence. This is use of reason is regulative only: "We ought not to derive the order and systematic unity of the world from a supreme intelligence, but to obtain from the idea of a supremely wise cause the rule according to which reason in connecting empirical causes and effects in the world may be employed to best advantage, and in such manner as to secure satisfaction of its own demands" (A673/B701).
This allows us to view the natural world as purposive, opening the way for teleological explanations, as in physiology. For example, "everything in an animal has its use, and subserves some good purpose" (A688/B716). One must always be careful not to treat such teleological connections as constitutive, but only as an aid to understanding. And we cannot assume from their use that an Author of nature exists. The transcendental object underlying the natural world remains unknown.
There are also regulative uses of reason connected to the ideas of the soul and of the world. We can treat our mental states "as if the mind were a simple substance which persists with personal identity (in this life at least), while its states, to which those of the body belong only as outer conditions, are in continual change" (A672/B700). And we can treat the series of outer appearances as if it is endless.
The subject of most of the Transcendental Dialectic is the speculative use of reason. In its speculative use, reason attempts to bring what is under the the scope of its ideas. In its practical use, on the other hand, reason is concerned with what ought to be, which has no necessary connection to what is. Practical reason is concerned with the question: what ought I to do? In the Preface to the second edition, Kant stated that his criticism of metaphysics has "a positive and very important use," (Bxxv) in that it removes obstacles threatening to destroy practical reason. Certain metaphysical doctrines, namely, "materialism, fatalism, [and] atheism" (Bxxxiv) must be curbed in the interests of practical reason, and the critique of metaphysics serves to police the realm of the practical against incursion from metaphysics. "The dogmatism of metaphysics, that is, the preconception that it is possible to make headway in metaphysics without a previous criticism of pure reason, is the source of all that unbelief, always very dogmatic, which wars against morality" (Bxxx).
Morality for Kant is action whose motivation is fulfillment of the moral law. The moral law itself is an a priori principle of practical reason, which applies to every rational being. An empirical law would be a "maxim" directing one to undertake certain actions in order to fulfill some other end, e.g. you ought to save money for your retirement. An a priori rule of conduct must abstract from all empirical ends. Fulfillment of the law is an end in itself. Thus the law will be formal, rather than material, stating that one ought to act in such a way that the principle of one's action can be universally applied to everyone. This is Kant's famous categorical imperative. The most obvious threat to the moral law that of fatalism, which Kant took to be incompatible with freedom, which in turn is an absolutely necessary condition for morality. "If there were no freedom, the moral law would never have been encountered in us" (Critique of Practical Reason, Preface, Footnote 1). In the absence of freedom, there is no sense in any rule that says that one ought to act in a certain way, since there is only one way in which an agent can act. In the natural world there is no freedom, but each event is necessitated by prior conditions. "It is just as absurd to ask what ought to happen in the natural world as to ask what properites a circle ought to have."
Materialism and atheism are complementary threats to morality, though not in such a fundamental way. If materialism is true, the soul is not immortal, and if atheism is true, there is no divine justice. Kant held that both immortality and a just proportion of happiness to virtue are components of the moral idea of the highest good. Thus under the assumption of materialism and/or atheism, the highest good cannot be realized and the object of morality is unattainable.
Speculative reason can do no more than secure the logical possibility of freedom, immortality and God. There is no contradiction in any of the concepts, because they pertain to things in themselves, which are not subject to the conditions of experience. As the actions of an empirical subject, my actions are determined by causal laws, but as transcendental subject, they may be transcendentally free. As an object in time, I have a limited span of life, but as transcendental object I am not determined in time at all. God can never be met with in any experience, be invoked as a necessary condition for experience, or proved a priori to exist. But a most real being is at least minimally thinkable. In the case of freedom, "morality does not, indeed, require that freedom should be understood, but only that it should not contradict itself, and so should at least allow of being thought" (Bxxix).
The transcendental ideas of God and immortality are relatively easy to accommodate on Kant's scheme, since their their objects (assuming they have objects) are transcendent. An immortal soul and a most real being are objects may in some unknown way be conditions of experience (of ourselves and of the world, respectively). But we need not be concerned to establish any connection between these objects and the objects of experience.
On the other hand, the idea of freedom requires a connection to experience. The reason is that events in the empirical world are thought as being caused by free actions, which themselves are only intelligible. "There is nothing to prevent us from ascribing to this transcendental object, besides the quality in terms of which it apears, a causality [action] which is not appearance, though its effect is to be met with in apperarance" (A539/B567). Kant's reconciliation of freedom with natural necessity requires that one and the same event is the effect of two distinct causalities: the action of an empirical object through laws of nature, and the action of the transcendental object in a way that is not determined by empirical laws.
The source of the purely intelligible causality of human beings is said to be practical reason. Thus an action is undertaken not because of prior conditions determining it to take place, but because it is an action which ought to be undertaken. We impose on our actions imperatives. Thus practical reason serves as an intelligible ground for human action. "This 'ought' expresses a possible action the ground of which cannot be anhything but a mere concept; whereas in the case of merely natural action the ground must always be an appearance" (A547/B575). In this way, practical reason can be seen as a cause, and its "causality," the action which brings about the effect, stands outside of time. Because it is outside of time, it does not begin to be and hence is not subject to the conditions governing beginnings in time. "Reason therefore acts freely; it is not dynamically determined in the chain of natural causes through either outer or inner ground antecedent in time" (A553/B581). Nonetheless, it is "the power of originating a series of events" (A554/B582) in such a way that its actions require no temporally antecedent conditions.
This has immediate consequences for morality. If a man tells a lie, we cannot assign blame to him by appealing to his "empirical character," as determined by natural circumstances. We can perfectly well explain an action as being determined in light of "defective education, bad company, . . . the viciousness of a natural disposition insensitive to shame, . . . levity and thoughtlessness" (A554/B582) and any other relevant factors. All this determines the man to behave as he has. "But although we believe that the action is thus determined, we none the less blame the agent, not indeed on account of his unhappy disposition, nor on account of the circumstances that have influenced him, nor even on account of his previous way of life; for we presuppose that we can leave out of consideation what this way of life may have been, that we can regard the past series of conditions as not having occured and the act as being completely unconditinoed by any preceding state, just as if the agent in and by himself began in this action an entirely new series of consequences" ( A555/B583, my emphasis). The causality of his reason, by which the man acted according to fulfill an end, is regarded "as complete in itself." At any time, regardless of past conditions and empirical laws, a man is free to act morally or immorally, in accordance with the moral law or in opposition to it. We do not know how this is possible, but we are able to think it as possible.
The relation of the ideas of the soul and God to morality are not so straightforward. They are said to be conditions of the highest good, whose attainment is the highest end of practical reason. Kant described the highest good in the following way: "virtue and happiness together . . . and happiness in exact proportion to morality" for the whole world of moral agents. The moral law presupposes the possibility of the attainment of hte highest good, lest "the moral law which commands that it be furthered . . . be fantastic, directed to empty imaginary ends, and consequently inherently false" (Critique of Practical Reason, Dialectic, I).
The immortality of the soul is a postulate of pure practical reason, as a condition for the possibility of the highest good. The maximization of virtue requires that the will of an individual be in complete conformity to the moral law, which is impossible in this life. "It can be found only in an endless progression to that complete fitness" of the will to the law (Critique of Practical Reason, Dialectic, IV). Aside for being necessary for morality, this postulate is a pillar of religion, as promoting holiness of the will.
God's existence is postulated to account for the possibility of happiness in proportion to virtue. Only a supreme cause of nature is capable of apportioning things in this way, since a reason for this proportionality cannot be found in nature itself. Such a cause must have will (its causality) and understanding (so that it can act in accordance with the idea of laws. Since it is our duty to promote the highest good, and necessary to postualte God's existence to account for its possible fulfillment, "it is morally necessary to assume the existence of God" ( (Critique of Practical Reason, Dialectic, V)