The final chapter of Book II of the Dialectic (“On the Dialectical Inferences of Pure Reason”) is entitled “The Ideal of Pure Reason.” Here the concept of pure reason is an “ideal,” which Kant distinguishes from the transcendental “ideas” of the soul and the totality of the world, covered in the first two chapters. The purported object of the ideal of pure reason is a most real being (ens realissimum), which is identified with God. The bulk of the chapter examines and criticizes three alleged proofs
for the existence of God: the physicotheological, the cosmological, and the ontological.
Thus far in the Dialectic, we have been dealing with transcendental ideas, which are concepts of pure reason. These concepts have as their intended objects beings which cannot come before us in experience. The Paralogisms took as its “text” the I as thinking being, arguing that it is determined by the concepts of substance, simplicity, personality and communion. The idea that is the subject of the Antinomy is the world, the totality of various series of conditions in appearances, which is determined by such concepts as magnitude. In both cases, the ideas are ways of thinking objects which are given to us through intuition: inner intuition in the case of the I
and outer intuition in the case of the world.
The Fourth Antinomy, according to Kant, gives us reason to depart altogether from what is given in appearance and apply the category of necessity to a purely intelligible object (which elsewhere would be called a “noumenon”) (A566/B594). Since an intelligible necessary being cannot be given through any appearance, we can only cognize it through an idea. When this is done, one specifies an object entirely through an idea. When an object is cognized purely conceptually, the cognition is an ideal: “an idea . . . as an individual thing determinable or even determined by the idea alone” (A568/B596).
Kant gives as an example of an ideal “humanity in its entire perfection,” which would only be realized in a single individual (A568/B596). The ancient Stoic philosophers embodied a more specific version of this ideal in the wise person, “a human being who exists only in one’s thoughts but is completely congruent with the idea of wisdom” (A569/B597). The wise person serves as a model or standard by which to judge the behavior and beliefs of people with imperfect wisdom.
After introducing the notion of an ideal as such, Kant turns to “transcendental ideal” (prototypon transcendentale). As “transcendental,” such an ideal is a priori, unlike the ideal of humanity, which is empirical. It is an “original concept” (Urbegriff) that is a product of human reason alone (A573/B601). Specifically, the ideal of pure reason is that of “the sum of all possibility.”
Reason seeks the sum of all possibility in order to attain completeness in its presentation of reality. It is an “unconditioned” that is the condition of everything that is itself conditioned. Reason generates a “principle of thoroughgoing determination,” according to which a condition for every object is that for every possible predicate, it must bear that predicate or its opposite. Reason requires that the condition would be met only if there is a being which supplies, as Kant puts it, the “material” for the determination of the thing. Such a being would be, in this respect, unconditioned, in that it would be throughgoingly determined without reference to any other being. If it existed, this being would be the basis of the possibility of all other beings. As such, it “would prove an affinity of all possible things through the identity of the basis of their thoroughgoing determination” (A573/B601, and see Kant’s pre-critical essay The Only Possible Basis of Proof for Demonstrating the Existence of God,
1763).
Here is a sketch of how determination through the sum of all possibilities is supposed to work. In standard cases, such as that of an individual human, some of the predicates of a being are positive and some are negative. Negative concepts are said to be mere limitations of positive concepts, so our thought of the object must be determined ultimately by reference to positive concepts. Some of these concepts will be a priori in character. Through positive concepts we “present a being” while through negative concepts we present “a mere not-being” (A574/B602).
Reason requires that the presentation of a being through positive concepts be based on “a transcendental substratum in our reason—substratum that contains, as it were, the entire supply of the material from which all possible predicates of things can be obtained” (A575/B603). In that case, this substratum is “the idea of a total of reality” (A575-6/B603-4). The idea of such a being would be of a “most real being” (ens realissimum), an ideal being which is a thing in itself. (Note that here, “thing in itself” is not what remains when the relation of appearance to sensibility is left out of account. A better expression would be “noumenon.”) This ideal would be the standard of all possibility, and there can therefore only be one such ideal.
After the ideal of a most real being has been given its initial explanation, Kant tries to tie it to the disjunctive syllogism as a form of inference. This move is made in order to justify the claim made at the beginning of the Dialectic that transcendental ideas are generated from basic forms of inference. The major premise in a disjunctive syllogism is an exclusive and exhaustive disjunction of the form “S is either A or B or C or . . ..” Semantically, this divides the “sphere” of possible predicates for the subject concept S among the extensions of the various predicates. If we say that S is not A, we have eliminated from the sphere of possible predicates of the subject S the extension of the predicate A, and then we can conclude that S is B or C, and so on for the other possible extensions. In this way, by excluding a possibility, the thought of S is made more determinate. For example, the sphere of the concept triangle is limited to equilateral, isosceles and scalene. If we have the information that at least two sides of a given triangle are equal, scalene can be eliminated, and the concept of that triangle becomes more determinate.
Now consider the application of the principle of the thoroughgoing determination of things, according to which each thing is determined with respect to every predicate or its opposite. We cannot use disjunctive syllogism as such in making this determination, since we must start the process of determination with the completely indeterminate concept “of a reality as such” (A577/B605). There is no list of predicates available a priori for the division of the sphere of possibility of a reality as such,
since “without experience one is not acquainted with any determinate kinds of reality that would be contained under that genus” (A577/B605). So how can the fully abstract concept of reality as such be determined?
The answer is that reference must be made to a special kind of being which contains within itself all predicates that can be thought a priori, a “total of reality” (A577/B605). We determine thoroughgoingly any being as such by limitation of what is thought in the totality of reality: “some of this reality is attributed to the thing but the rest is excluded” (A577/B605). Although this procedure is analogous to the use of disjunctive syllogism, it is not quite the same. Rather than determining the object by excluding predicates that might belong to it, the procedure excludes, so to speak, portions of the sum total of reality. When this procedure is completed, all the predicates of the object are set, and the object is thoroughgoingly determined. For example, a portion of the figures found in the totality of reality are solid (three-dimensional) and a portion of it are plane (two-dimensional). When we think of a triangle, we exclude the portion of the totality of reality that is solid. This makes the concept of a triangle more determinate (narrowed-down) than that of a figure. We then exclude the open plane figures, and finally those that have more or fewer than three sides. As Kant puts it, this use of reason is analogous to the the use according to which it proceeds in disjunctive syllogism
(A577/B605).
The ideal is not thought in this way as presenting an existing being. Instead, it provides a prototype for existing things, which measure up more or less to that ideal, though they are “always infinitely far from attaining it” (A578/B606). All objects are determined in their possibility based on the ideal. Even the negative concepts we apply to objects express only limitations of the “supreme reality; hence they presuppose this reality and are merely derived from it as regards their content” (A578/B606). Kant makes an analogy here between things as limitations of the most real being and figures which are limitations of infinite space.
Because of the relation of all other beings to the most real being as limitations of it, the ideal is “original being” (A578/B606). It is also “supreme being” because none is higher, and “being of all beings,” because everything is subject to it. Calling it “being,” though, only indicates that it is an ideal, a concept of an individual, not that it exists.
We must also not be misled by the talk of limitation of one being by another into thinking that the supreme being is somehow divided into subordinate beings. (Compare Spinoza’s claim in the Ethics that substance is not capable of division (Part I, Proposition 13).) The ideal of a sum of all reality does not indicate a literal composition. The relation of the ideal to the subordinate beings is that of being their basis or ground (Grund
). Included among the beings based on the ideal are the objects of human sensibility, which is clearly not a part of the supreme being.
One may go further and treat the ideal as more than a mere concept, but rather as referring to a being, thereby “hypostatizing” it or making it into a being (A580/B608). Then predicates, such as being “single, simple, all-sufficient, eternal, etc.,” may be applied to this hypostatized being (A580/B608). The result is the concept of God. So the transcendental ideal of pure reason, which is the basis for a priori determination of objects, is the foundation of a doctrine of rational theology.
Thus rational theology treats the concept of a totality of being as a thing, as if it were given objectively. But this is an improper procedure, since the point of the ideal was only to “integrate and realize the manifold of our idea in an ideal regarded as a separate being” (A580/B609). The ideal is a mere invention, and we have no right even to assume the possibility of such a thing. And we cannot draw any inferences from it either, including the very use for which the ideal was intended, “the thoroughgoing determination of things as such” (A580/B608). To try to do so results in an illusion.
The illusion is a consequence of an extrapolation from the way in which we determine what are possible objects of experience. We take as our basis “the single, all-encompassing experience,” which is regarded “as given in one sum” (A582/B610). The illusion is to think that this kind of procedure can be applied to objects as such, which then would require an absolute sum on which to base their possibility. Moreover, we think of the sum of experience not in the proper sense of coherence according to rules, but improperly (as in the Antinomy) as a single entity, which leads naturally to regarding the ideal of a sum of all reality as a single entity as well.
This rather arcane description of how pure reason arrives at the existence of God hardly explains why people have been persuaded by arguments that God exists. Something else motivates people to seek a highest being, namely, the search for an ultimate explanation of common experience.
In his preliminary remarks (Section III of Chapter III), Kant gives a preview of what is to come. The problem of reason is to explain contingency, and it can do so only by postulating a necessary being. But where is it to find a concept of a necessary being? It must be a being with no limitations, whose concept “contains within itself the therefore for every wherefore” (A585/B613). (That is, when we ask for the reason or purpose (wherefore
) of something, an answer (therefore
) is always forthcoming.) In this way, the being is all-sufficient. This would be a being of supreme reality, which contains the basis of all possibility. Any other being, while perhaps not dependent on that being, is at least dependent on something, and hence would not qualify as the necessary being.
If we were forced into deciding which being is the necessary being, the supreme being would be the best choice. But no rational proofs force us to choose. For a limited being could still fulfill the role of necessary being, that is, a being which has no other being as the basis of its existence. The lack of a proof that the necessary being is the supreme being does not mean that we have no reason to believe that one exists. The interests of morality, which motivate our practical reason, may induce us to make the choice that theoretical or speculative reason does not.
Even the most common human mind follows the course of reasoning leading up to the supreme being. Things happen and we want to know why. We explain their occurrence by appeal to a cause, and we pursue the chain of causes, looking for a highest cause. The end of our quest seems best located in a supreme or highest causality, which in turn is understood as the causality of an all-sufficient or perfect being, the God of monotheism. Kant notes that even polytheists have a touch of monotheism in them, which indicates that this reasoning is based on “common understanding’s natural course” (A590/B618).
According to Kant there are exactly three types of proof of God’s existence that are based on pure theoretical reason. The first begins with determinate experience and seeks an explanation of its character. This is the physicotheological proof. The second begins with indeterminate experience, the mere existence of contingent beings, and seeks a necessary being. This is the cosmological proof. The third abstracts from experience altogether and begins with pure concepts, reasoning to the existence of a supreme being from those concepts. This is the ontological proof, which is transcendental
in that it has no empirical basis whatsoever.
Kant examines these proofs in the reverse order from the one in which they are presented. He begins with the transcendental proof because it alone provides, on its own, the concept of God as the most real being. It is this concept which guides reason in this its endeavor and what in all such attempts marks out the goal reason has set for itself
(A591/B619). The experience-based (or theistic) proofs look for explanations, but even if found, the explanatory being or beings need not be identified with God. (See Hume’s Dialogues concerning Natural Religion for arguments to this effect. In the Prolegomena, Kant calls Hume’s arguments against theism very strong
(§57, Ak 4:356).)
The ontological proof for the existence of God was offered by the Italian monk Anselm of Canterbury, in the Proslogion, written in the 11th century. It was criticized in the 14th century by Thomas Aquinas, whose own five proofs for God’s existence all begin with experience. Descartes revived the proof in the 17th century, and Kant refers to it as “the famous ontological (Cartesian) proof of the existence of as supreme being from mere concepts” (A602/B630). It is found as well in Leibniz. As noted, Kant treats this proof first because it takes as its starting-point the concept of a supreme being, which is what “guides” reason in its attempts to find completeness in that concept (A591/B619).
The treatment of the ontological proof consists of two steps. The first is to show that in general it is impossible to conclude from any concept that it refers necessarily to an object. The second is to apply this result to the ontological proof, which Kant thought shows the proof to be a waste of effort (A602/B630).
We can begin by noting that the ontological proof attempts to establish the existence of a being merely from the premise that we possess, a priori, a concept of a being of that kind. The only way in which this could be done is by claiming that there is a contradiction in any attempt to think such a being as not existing. By analogy, it is claimed, there is a contradiction in the attempted thought of a triangle which does not have three sides.
Kant notes that such analogies are of no value in showing how the attempt to think the non-existence of any being could be contradictory. Consider the mathematical judgment that a triangle has three sides. We can say that the predicate has three sides attaches necessarily to the subject triangle, in the sense that denying the predicate of the subject entails a contradiction. This is what Kant calls “a conditioned necessity of . . . the predicate in the judgment” (A593/B621). The condition under which having three sides is necessary is the subject of the judgment, a triangle.
Unconditioned or absolute necessity (that whose denial is a contradiction) does not hold in the triangle case. There is no contradiction in the thought of a square that has four sides. So we cannot say that a three-sided object is an absolutely necessary being, one whose non-existence entails a contradiction. If we deny that there is a three-sided thing (“annul the predicate”), all we have done is to deny that there is a triangle as well (we “annul the subject”).
The same considerations hold if we try to treat existence as the predicate in a judgment of the form A being with property F exists. Suppose (for the sake of argument) that one could not deny existence of a being with property F without contradicting oneself. Then if one were to take away the predicate, existence, one would take away along with it the subject, a being with propery F. “If you annul the being’s existence, then you annul the thing itself with all its predicates. Whence, then, is the contradiction to come?” (A595/B623).
So the only avenue left is to hold that the subject, a being with property F, is the sort of being which can never be annulled. If annulling its existence annuls the being of the subject, then the existence of the subject could not be annulled, and such a being would exist necessarily. But a subject whose existence cannot be annulled is precisely a necessarily existing being. So claiming that the subject cannot be annulled begs the question against anyone not convinced that there is a necessarily existing being.
Now that Kant has made his general case against the ontological proof, he considers what the proof would look like if the schematic reference to property F is filled in. The claim of the ontological proof is that a being with maximal reality exists necessarily. The argument as given by Kant at A596-7/B624-5 can be reconstructed as follows (with the content of concepts displayed in italics).
On the other hand, Kant emphatically denies step 5, which is needed to discharge the antecedent in step 6. In fact, he claims that there is an inconsistency in conjoining steps 3 and 4: “You have already committed a contradiction if, in offering the concept of a thing that you wanted to think merely as regards its possibility, you have already brought into this concept—no matter under what covert name—the concept of a thing’s existence” (A597/B625). This is a somewhat cryptic comment that requires further discussion.
We can better understand Kant’s claim if it is framed in the form of a dilemma. If one is conceiving a being as possible in the sense that its concept contains no contradiction, then one’s concept of the object does not contain existence. The use of the argument for step 3 requires the rejection of step 4. Kant will argue against step 8 on the grounds that existence is not a part of the concept of a thing, but that argument applies equally well against the consistency of the move from step 1 to step 3 and step 4.
On the other hand, if existence is really thought in the concept of a maximal reality, perhaps on the grounds that the concept of reality implies that of existence, then step 3, along with the rest of the argument, is redundant. (A further possibility is simply that 4 is true because the concept of a being with maximal reality exists, which does not lead to what was to be proved.)
The reason the rest of the argument is redundant is that “you have presupposed an existence as belonging to possibility, and have then allegedly inferred the thing’s existence from the thing’s intrinsic possibility—which is nothing but a pitiful tautology” (A597/B625). Here is one way to think of this claim. In proving that a maximal reality is possible, one must prove that there is no contradiction in all the characteristics which make up its concept, which includes existence. In that case, one is already claiming that the existence of such a being is included in its possibility. The argument is dressed up to look as if one establishes the possibility by looking at the other characteristics besides existence, then discovering existence there as a kind of bonus.
The correct way to understand judgments of existence is that they are synthetic. But if so, then step 9 is false. We can annul the existence of a being with maximal reality without annulling the possibility of a being with maximal reality. This is because without existence being built into the concept of a maximal reality, there is no contradiction in the denial of its existence. Annulling the existence of a being with maximal reality does not result in a contradiction, then. “If you admit—as any reasonable person must—that any existential proposition is synthetic, then how can you assert that the predicate of existence cannot be annulled without contradiction” (A598/B626)?
Another way of putting the point here is by saying that, “Being is obviously not a real predicate, i.e., it is not a concept of anything that can be added to the concept of a thing” (A598/B626). When we use “being” as a logical predicate, by saying, for example, “God is,” we are only positing (affirming the existence of) an object to which the concept (in this case, being God) refers. The properties thought in the concept and the properties of an existing object to which it refers are exactly the same. If they were not, if some property was missing. then the thought of the object would be inadequate. “An actual hundred thalers do not contain the least more than a hundred possible thalers” (A599/B627). Similarly, the concept of a maximal reality can be thought without any implications for whether an object corresponding to it exists.
What allows us to posit an object corresponding to a concept, to affirm that the concept has reference, is something that does not lie in the concept itself. “In the case of objects of the senses this is done through the coherence of these objects, according to empirical laws, with some of my perceptions” (A610/B629; compare the understanding’s postulate of actuality, What coheres with the material conditions of experience (with sensation) is actual
(A218/B266)). Such an appeal is inadmissible in the present case, however. We have no basis for making any assertion about what exists beyond the reach of perception. In fact, the original concession of step 2 is now retracted. We cannot even judge as to the possibility of a being with maximal reality, since “the mark of the possibility of synthetic connections must always be sought only in experience” (A602/B630).
The ultimate diagnosis of the failure of the ontological proof is given at the beginning of the next section. According to Kant, philosophers agreed on the need to postulate a necessary being, but they needed as well to give a description of such a being. The natural choice was a being with maximal reality. “But people concealed this natural course of reason, and instead of ending with this concept, they tried to start from it in order to derive from it the necessity of existence which the concept was, after all, determined only to supplement” (A603-4/B631-2). The result is an argument that is “a mere innovation of school wit” that “brings with it nothing satisfactory, either for sound and natural understanding or for any examination that complies with school standards” (A603-4/B631-2).
The cosmological proof moves from the existence of contingent beings to the existence of a necessary being. It was the third of the “five ways” of Aquinas and was mobilized frequently by Leibniz (e.g. “Monadology,” §§ 36-38). Wolff made it central to his treatment of rational theology (Theologiae Naturalis, Part 1, Chapter 1). The Fourth Antinomy had already ruled out any proof of the existence of a necessary being as part of the world. Now it is to be shown that there can be no proof that a necessary being exists outside the world, either.
The cosmological proof may be reconstructed as follows.
As we have just seen, Kant thought that the cosmological proof is not finished after the attempted proof of the existence of a necessary being, since a necessary being need not be God. It is required to describe the necessary being in a way that conforms to the notion of God, whose existence is to be proved. This leads to a second argument to the conclusion that the required necessary being is a being with maximal reality (ens realissimum). Here, experience is of no value at all, and we are left with pure reason as the “witness” to what such a necessary being is.
The first problem with step 4 can be better seen in its consequence, which Kant calls “the nerve of the proof” (A608/B636), step 5. Kant claims that this step presupposes that “the concept of a being of supreme reality is completely adequate to the concept of absolute necessity of existence” (A607/B635). This, Kant goes on, is the same as saying that “the absolute necessity of existence can be inferred from supreme reality” (A607/B635). And this last claim is “a proposition that was asserted by the ontological argument,” in which case “the ontological proof, although it was to have been avoided, is in fact being assumed and laid at the basis of the cosmological proof” (A607/B635).
The case is not well-stated, however. What the ontological argument asserts is that absolute necessity of existence can be inferred from the concept of supreme reality. That is, if a supreme reality is possible (and so thinkable in a concept), then “among all possible things there is one which carries with it absolute necessity” (A607/B635). So appeal to the concept of a being with maximal reality makes the cosmological proof superfluous, since the proof of a necessarily existing being is not sufficient to establish the existence of God, and what fills the gap can be used to prove that there is a necessarily existing being. Kant puts the matter better when he says that “the ontological proof alone, conducted from mere concepts, is what contains all the cogency in the so-called cosmological proof” (A607/B635).
Kant goes on to cite briefly several major flaws in the argument. The first is that step 4 of the argument purports to establish the existence of a necessary being. It was shown in the Fourth Antinomy that any contingent being among appearances can depend only on some other contingent being which itself is an appearance. So the first disjunct is not in fact a possibility. This in turn invalidates the use of disjunctive syllogism in step 7.
A further problem arises from the fact that the completion of the series of appearances (even if that is granted) by a necessary being is not absolute completeness. That is, even if we were to grant that the series of causes of appearances terminates in a being whose existence does not depend on some other appearance, such a being need not be absolutely necessary. It is necessary only relative to the appearances.
The final problem is carried over from the criticism of the ontological proof. The concept of a being with maximal reality is allowable because such a being is logically possible. But we have no way of establishing its real possibility.
Reason falls into these errors because it confuses what it postulates to satisfy its need for unity with the existence of a unifying being. In fact, in all its endeavors, the understanding will never reach a necessary being. So we can only take completeness to be a rule to guide us in our investigations: “You ought to philosophize in such a way about nature as if for everything belonging to existence there is a necessary first basis” (A616/B644).
This must be tempered by a conservative rule “not to assume any determination pertaining to the existence of things as being such a highest basis—i.e., as being absolutely necessary—but to continue keeping your path open to further derivation” (A617/B645). To follow both rules consistently requires the location outside the world of the basis of the existence of the world and things in it.
Kant goes so far as to claim that the rule of unity is what must have guided ancient philosophers who asserted that the existence of matter is not contingent. Kant notes (in a Humean vein) that it is possible to think the non-existence of matter. So the necessity of matter lies “only in thought” and the claim of its necessity “must have been based on a certain regulative principle” (A618/B646).
Modern philosophers in the seventeenth and eighteenth centuries recognize extension and impenetrability as exhausting the concept of matter, so extension and impenetrability are the highest principles of the unity of material things. But there is no absolute necessity in appearances, and reason must appeal to an original being for a principle of unity. Although this principle is only regulative, reason mistakes it as being constitutive. We can see this in the fact that the highest being cannot be conceptualized as “a thing by itself,” and necessity is only “as a formal condition of thinking” (A620/B648).
The final proof for God’s existence appeals to determinate experience, specifically to the “character and arrangement” of the things in the world (A620/B648). This proof had been subjected to severe criticism in Hume’s Dialogues Concerning Natural Religion, which Kant discussed at some length in the Prolegomena (§ 58, Ak 4:357-360). Kant asks for respect for this proof, in that it “is the oldest, clearest, and most commensurate with common human reason” (A623/B651).
Kant describes the proof as having four “chief moments” (A625/B653). The first is the ubiquitous “signs of arrangement carried out with great wisdom according to a determinate aim” (A625/B653). The second is that this aim attaches to the things contingently, and not by virtue of the character of the things themselves. From this is drawn the conclusion (the third moment) that there is a cause or causes, acting through freedom, of the arrangement. Finally, there is only one such cause, given the reciprocal harmony among all the things we find arranged “as members of an artistic structure” (A626/B654).
The argument appeals to an analogy between nature and human artifact. Just as the human artist gives order and purpose to what he constructs from natural materials, the suprahuman artist gives order and purpose to all of nature. Kant notes that the analogy could at best establish that there is an “architect of the world,” and not that there is a “creator of the world” (A627/B655).
The only way to get a grasp of what such an architect would be like is to resort to absolute predicates, “a being possessing all power, wisdom, etc.” (A628/B656). If we were to use predicates taken from experience, they would be intolerably vague: “such predicates as very great, or amazing or immense power and excellence provide no determinate concept at all” (A628/B656).
The physicotheological proof is easily dismissed on the grounds that no experience can ever be adequate to “the transcendental idea of a necessary and all-sufficient being” (A621/B648). On the other hand, we can only comprehend the order, purposiveness, and beauty of the world by postulating a being in whom all perfection is united. There is no contradiction in the concept of such a being, nor is there a contradiction in thinking its relation to the world.
The belief in a perfect being informs our scientific investigation, which in turn produces more evidence of order and purpose, which reinforces the belief in a basis for organization to the point where it becomes “an irresistible conviction” (A624/B652). Any attempt to dismiss the proof will be ineffective once one turns one’s gaze upon “the marvels of nature and upon the majesty of the world edifice” (A624/B652).
At the same time, the proponent of the physicotheological proof must not put down the cosmological or ontological proofs “as the cobweb of gloomy ponderers” (A629/B657). He must recognize that the proof cannot yield “apodeictic certainty,” (A624/B652) and requires supplementation by the cosmological, and ultimately the ontological proofs (A629-30/B657-8). The only feature of the world that even possibly allows a leap beyond it is its contingency.
The Transcendental Ideal concludes with a section in which Kant offers a number of definitions and with them a final pronouncement on the possibility of theology.
Theology itself is “the cognition of the original being,” which can be either a thought through pure concepts, in which case the theology is transcendental, or a thought from concepts borrowed from experience, as in natural theology (A631/B659). The transcendental theologian, who claims nothing more than that there is a God, is a deist, while a natural theologian, who believes there is a living God, is a theist. (For more on deism and theism, see Prolegomena, Conclusion §§57-58, Ak 4:355-360.)
A further distinction is between theoretical and practical cognition. The former concerns itself with what is, and the latter with what ought to be. Kant will later in the Critique (in the Doctrine of Method) argue for a practical theology based on the moral law. He has so far been concerned with theology in a theoretical sense. This theology is speculative if it concerns an object that cannot be found in experience. But efforts of speculative theology are “entirely fruitless,” so that “unless moral laws are laid at the basis or used as a guide, there can be no theology of reason at all” (A636/B664).
Still, speculative theology has an important negative use. This is as a corrective to any concept of a supreme being that might be generated by appeal to appearances (objects of experience). Although it cannot prove the existence of “a supreme and all-sufficient being as highest intellegence,” speculative theology does show this to be the only legitimate concept of a deity (A640/B668). Specifically, speculative theology allows the exclusion of atheism, deism, and anthropomorphism. Atheism is excluded because we have as little right to deny speculatively the existence of a supreme being as to assert it. Deism is blocked for the similar reason that there are no grounds for holding that the a supreme being has no properties with which we are familiar. Anthropomorphism is a positive doctrine that attributes to God properties of sensuous beings, and it has no grounds so long as the physicotheological proof fails.
If practical reason is to supply what theoretical reason cannot, i.e., proof of the existence of a supreme being, theoretical reason stands ready with a battery of transcendental predicates at the disposal of theistic moral theology.
Necessity, infinity, unity, existence outside the world (rather than as world soul), eternity without conditions of time, omnipresence without conditions of space, omnipotence, etc.: all of these are transcendental predicates; and hence the purified concept of them, which any theology needs so very much, can be obtained only from transcendental theology. (A641-2/B669-70)