2. The Possibility Proof and the Proof A Posteriori in Beweisgrund

In Beweisgrund, Kant discusses two proofs in detail.Footnote ⁸ The first section of Beweisgrund is dedicated to what is known as the ‘possibility proof’. In its most simple form, the proof, which runs from the sheer possibility of something to God's existence, can be summarized as follows:

1. (1) Something is possible.

2. (2) If something is possible, then this possibility must be grounded in an absolutely necessary being.

3. (3) There is an absolutely necessary being that grounds all possibility.

4. (4) If there is an absolutely necessary being that grounds all possibility, this being is God.

5. (5) God exists.

So the possibility proof consists of two main steps: first, it argues for the existence of an absolutely necessary being as the ground of possibility, and then it shows that this being is God. The literature is full of discussion about potential problems of the proof and how they could be avoided, but this is not my business here.Footnote ⁹ I can also abstract from the hotly debated topic how God grounds possibility. Yet, there is one point that is relevant for my purposes. Some proponents of the debate hold that the God of the possibility proof grounds all realities by instantiating them, which faces the threat of Spinozism, according to which (as Kant understood it) the world is God.Footnote ¹⁰ However, Kant holds that God contains the ‘ultimate real ground of all other possibility’ (OPA, 2: 83; cf. 2: 79, 85, 87) and argues that these worldly possibilities are not instantiated by God (2: 85–6). This rules out that God instantiates all possibilities and is, in effect, identical to the world.Footnote ¹¹

The second proof is the topic of the very lengthy second section of Beweisgrund, and Kant introduces this proof by way of concluding the first section:Footnote ¹²

The possibility proof is a priori because it derives the consequence of God's creation from his essence, by which he grounds them. The second proof, by contrast, is a posteriori because it derives God as the ground of the world from the consequences.Footnote ¹³ Thus, I will call this proof the ‘proof a posteriori’, which considers the great harmony in the essences of thingsFootnote ¹⁴ and concludes that they must be grounded in an absolutely necessary being. It is not really clear what logical form the proof a posteriori is supposed to have, but Kant says that in this proof ‘both the existence and the properties of itFootnote ¹⁵ are immediately inferred’ from experience (OPA, 2: 156). Thus, I assume that the proof can be summarized as follows:

1. (1) The actual world has a unified principle of its possibility.

2. (2) If the world has a unified principle of possibility, God (the absolutely necessary ground of the unity of possibility) exists.

3. (3) God exists.

Premise (1) is primarily based on the order of geometry (OPA, 2: 95–6) and mechanics (2: 99–100), insofar as the unity that we encounter there is ‘itself grounded in the possibilities of things’ (2: 125), as opposed to an order that ‘is considered contingent and originating from the choice of an intelligent being’ (2: 124). The difference between these kinds of orders is central here. The second order is called ‘moral’ because this order is contingent and depends on God's choice. By contrast, the first order is ‘non-moral’ (unmoralisch); the order is grounded in the natures of things and not dependent on God's choice, but his essence (2: 100). According to Kant, the moral order could at most prove the existence of a ‘craftsman, but not of a creator of the world’ (2: 123); so the proof a posteriori must be based on the non-moral order (2: 122–3, 124–5). Kant criticizes traditional physico-theology (the branch of theology that tries to cognize God through his supposed works) for merely considering the moral order (2: 116–23) and advocates an improved method of physico-theology that seeks out the non-moral order of the world (2: 123–37).

As regards premise (2), Kant answers the question, ‘Is this unity … possible without dependency from a wise author?’, by flatly responding, ‘The formal [aspect] of such great and manifold regularity prohibits this’ (2: 125). So Kant does not give an elaborate answer to the question why the great harmony of the world must be grounded by God. However, he does not consider the proof a posteriori to be sound anyway. Although Kant contends that the proof is ‘possible’ and ‘in every way worthy to be brought to proper perfection through united efforts’ (2: 159), he holds that the proof is ‘incapable of mathematical certainty and precision’ (2: 160).Footnote ¹⁶ The reason is that ‘we are not acquainted with all created things (alles Erschaffene)’ (2: 160), from which follows that we do not know if the world really has a unified principle of possibility. Premise (1) is therefore uncertain, even if highly probable; and as a result, the whole proof is uncertain – not even considering premise (2), which may also be problematic.

Again, I do not intend to discuss the two proofs in detail; I only outline them for the sake of discussing their afterlife in the Critique. Let us now turn to the first of the four threads of thought that I presented in the introduction.

3. The Procedure of Forming the Legitimate Concept of the Ens Realissimum

In section two of the Ideal, Kant describes a procedure of forming the ‘transcendental ideal’, that is, the concept of God. As this procedure is described at length by other authors (with whom I generally agree),Footnote ¹⁷ I only give a brief summary of it here. Every predicate is either positive or negative. Positive predicates are ‘transcendental affirmations’, whereas negative predicates are ‘transcendental negations’. Whilst a transcendental affirmation ‘expresses a being, and hence it is called reality (thinghood)’, a transcendental negation ‘signifies a mere lack’ of reality (A574–5/B602–3).Footnote ¹⁸ All realities taken together form the ‘all of reality’ (A575/B603); and the being that instantiates all realities is the ens realissimum (A576/B604), which is God. Thus, we attain the transcendental ideal (as the concept of God) by forming the concept that contains all transcendental affirmations.

However, Kant distinguishes between two conceptions of the ens realissimum:

Kant then rejects the first conception because it results in a self-contradictory concept of God.Footnote ¹⁹ As Kant argues in the Ideal, ‘our whole sensibility, including all reality in appearance … cannot belong to the idea of a highest being as an ingredient’ (A579/B607).Footnote ²⁰ Rather, ‘the highest reality would ground the possibility of all things as a ground and not as a sum total’ (A579/B607).Footnote ²¹ I can only give a sketch of Kant's argument here. God is not only the ens realissimum, but also the ‘original being’ (ens originarium), that is, the ‘origin of all things’ (PM, 20: 301). If the original being instantiated all realities, including sensible ones, ‘then the original being would be regarded as a mere aggregate of derivative beings’, which is ‘impossible’ (A579/B607). If we conceive of the ens realissimum as a sum total of reality, we end at Spinozism.Footnote ²² Thus, this conception of God is inconsistent and hence illegitimate.

According to the legitimate conception, on the contrary, the ens realissimum instantiates only so-called ‘pure’ realities and is the ground of all limited realities, just as in Beweisgrund. For having a reality is not a matter of an either-or. Rather, there are degrees of reality (they have an ‘intensive magnitude’, B207). Kant thinks that only God possesses ‘pure’ realities, that is, realities of the highest degree.Footnote ²³ All realities of things in space and time, on the contrary, are not pure, but limited: ‘there is no thing in the whole world that has pure reality’ (Th-Pölitz, 28: 1021).Footnote ²⁴ The notion of an ens realissimum as the sum total of all pure realities (and the ground of all others) is consistent, according to Kant, because pure realities cannot contradict each other.Footnote ²⁵ So it is only this conception that can legitimately be the object of belief or of proofs of God's existence.

It is not uncommon to read the formation of the transcendental ideal as a process that occurs by virtue of a natural illusion.Footnote ²⁶ But this strikes me as false. For the discussion of the formation of the transcendental ideal is already completed when Kant first uses the word ‘illusion’ (at A581/B609). Consequently, we should assume that the legitimate concept of God as the ground of possibility is formed independently of an illusion. As we shall see in section 5, there is nonetheless an illusion attached to this idea as well. But now let us turn to the infamously complex and difficult illusion that Kant describes at the end of section two of the Ideal. I will argue that this illusion only concerns the illegitimate conception of God.

4. The Natural Illusion Leading to the Illegitimate Conception of the Ens Realissimum

The second section of the Ideal not only provides a procedure by which the legitimate concept of God can be formed, but also deals with a natural illusion that arises from our subjective needs as regards the formation of concepts. These two issues are deeply interwoven. According to Kant, the ‘principle of thoroughgoing determination’ (PTD) requires that ‘among all possible predicates of things, insofar as they are compared with their opposites, one must apply to it’ (A571–2/B599–600). Since Kant later in the text clarifies that he is talking about transcendental affirmations and negations, the PTD holds in fact that everything is completely determined with regard to each pair of transcendental affirmations and their negations. A concept of a thing that is determined with respect to all of these pairs is called a ‘complete concept’ (A572/B600).Footnote ²⁷ The transcendental ideal, as the concept of the ens realissimum, represents the all of reality and is the sole complete concept that only has transcendental affirmations – this is how it is defined. But every complete concept of worldly things contains some transcendental affirmations along with some transcendental negations.

Now Kant holds that one can think the absence of reality only if one has a concept of this reality. For example, ‘The person blind from birth cannot form the least representation of darkness, because he has no representation of light’ (A575/B603). This lends a crucial role to the idea of an ‘all of reality’ that is the sum of all transcendental affirmations. All other concepts are limitations of the all of reality because they contain negations of some reality that belong to the all of reality. For this reason, Kant metaphorically refers to the all of reality as ‘the entire storehouse of material from which all possible predicates of things can be taken’ (A575/B603). But he insists:

What is noteworthy here is not only that this requirement of reason gives us no warrant for assuming God's existence, but also that the relation between the ‘unconditioned totality’ (the all of transcendental affirmations) and the ‘conditioned totality’ (the limited concepts) is one between concepts and not between things. This needs further explanation. The PTD demands of every possible reality that we are able to determine whether it belongs to a thing or not. For we can form a limited concept only by limiting an unlimited reality in thought; and if we assume that all unlimited realities can be limited,Footnote ²⁸ it follows that the legitimate concept of God (as the sum of all pure realities) must be possible if the totality of all limited concepts is to be possible. This does not mean that we must form the transcendental ideal before we can form limited concepts. Rather, it means that the possibility of the totality of all possible limited concepts presupposes the possibility of the totality of all possible unlimited concepts (that is, the transcendental ideal).

This is not a metaphysical grounding relation between God and the world, in the sense that God would ground possibility by instantiating the realities of worldly objects. Kant admits that his initial presentation of the relation between the all of reality and limited concepts suggests that this is the way God grounds possibility, but parenthetically remarks that this has only been the ‘first crude outline’ of the story (A579/B607). For ‘the derivation of all other possibility from this original being, strictly speaking, also cannot be regarded as a limitation of its highest reality and as a division, as it were, of it’ (A579/B607). God is not the ‘storehouse’ who grounds possibility by offering the material for limitation, but the ground of possibility outside the world.

Yet Kant's revision of the ‘first crude outline’ affects not only the grounding relation between God and the world, but also the grounding relation between the transcendental ideal and limited concepts. For Kant now says that the ‘manifoldness’ of worldly things ‘rests not on the limitation of the original being itself, but on its complete consequences’ (A579/B607).Footnote ²⁹ The ‘complete consequences’ of God are the world and everything that is possible through him (A579/B607). But this means that the ‘entire storehouse’ on which the limitation of concepts depends is the all of sensibleFootnote ³⁰ reality, not the all of pure reality that constitutes the legitimate concept of God.Footnote ³¹ As we shall see now, the all of sensible reality is at the heart of the infamous ‘illusion’ of reason (A581/B609) at the end of section two; and I shall argue that this illusion attempts to establish the existence of the ens realissimum in the flawed, Spinozistic sense.

Kant begins his discussion of the illusion by raising a question:

Crucially, the transcendental ideal (and the illusion attached to it) ‘is grounded on a natural and not a merely arbitrary idea’ (A581/B609). As Grier has pointed out, reason has an interest in pursuing the totality of conditions, even though we cannot reach it in experience. Therefore, the transcendental ideas of the soul, the world and God are necessary illusions – they seem to be the unconditioned that reason demands (and this semblance is unavoidable), but it would be an error to judge that the unconditioned is, or even could be, given in experience. So we have to distinguish between transcendental illusions, which are unavoidable but are not judgements, and transcendental errors, which are motivated by illusions but avoidable.Footnote ³³

The illusion in section two turns on the PTD.Footnote ³⁴ For we can form the complete concept of a thing only if we compare it with all possible sensible realities (as shown above). Thus, we must possess the concepts of all sensible realities in order to decide whether a transcendental affirmation or its negation applies to a given thing.Footnote ³⁵ Since we can become acquainted with realities only by experience,Footnote ³⁶ these realities must ‘be presupposed as given in one sum total’ (A582/B610) as the enabling condition of the formation of sensible concepts.Footnote ³⁷ Thus, Kant thinks that the conditioned totality of sensible concepts presupposes as its condition that all the realities represented by positive sensible concepts are actually instantiated. But there is an illusion involved in the argument that Kant does not make explicit, namely the illusion that we can in fact determine a complete concept.Footnote ³⁸ While introducing the PTD at the beginning of section two, he remarks:

Although the task for reason to form complete concepts cannot be fulfilled, the idea of a complete concept is a necessary illusion that serves as a regulative idea for the use of the understanding. Unfortunately, Kant does not say why this goal is unachievable. But as we have seen, it is a necessary condition of forming complete concepts that the all of sensible reality is given in a sum total. Since Kant speaks of the ‘idea of the sum total of all reality’ (A582/B610) and ideas are concepts of reason that can have no corresponding object in experience (A320/B377, A621/B649), this suggests that Kant thinks that the all of sensible reality can never be given in experience. But since reason can only form a complete concept if the all of sensible reality is given, we are prone to the illusion that the latter is the case.

However, this does not yet account for an illusion that God exists, which is only accomplished by a series of further illusions. First, we think that the sum total of the realities we can become acquainted with – that is, the sum total of sensible realities – is the sum total of realities in general. However, this is an illusion because the sum total of sensible realities does not include the noumenal realities of things in themselves, let alone the pure realities that are constitutive of the legitimate concept of God.Footnote ³⁹ And further illusions (that I do not need to discuss here) lead to mistaking this sum total of sensible realities for God (A582–3/B610–11). Hence, the illusory argument would establish not only that the all of sensible reality is grounded by God, but even that the all of these realities itself is God. This would establish Spinozism, which Kant condemns.

In conclusion, section two of the Ideal discusses four different grounding relations:

1. (i) the grounding relation by which the totality of the concepts of pure realities makes the totality of the concepts of limited realities possible;

2. (ii) the grounding relation by which the totality of positive sensible concepts makes the totality of sensible concepts possible;

3. (iii) the grounding relation by which the sum total of sensible realities makes the totality of sensible concepts possible;

4. (iv) the grounding relation by which God grounds worldly possibilities.

Relation (i) does not establish the existence of any object, but only the necessity of a particular concept; however, Kant ultimately sets this relation aside in favour of relation (ii) because sensible concepts are not limitations of pure realities.Footnote ⁴⁰ Relation (iii) figures in a transcendental illusion that we can actually determine the complete concept of a thing, but only further illusions make us identify the sum total of sensible realities with a Spinozistic God. Relation (iv) is only a by-product of Kant's discussion; he merely suggests that (iv) is part of the legitimate concept of God, and the transcendental illusion in section two does not involve this relation.

But if we look back to Beweisgrund, the possibility proof would establish (iv), but not the other grounding relations. Recall that this proof argues that there must be an absolutely necessary being that is the ground of worldly possibilities. This is an entirely different kind of grounding than grounding the possibility of concepts by providing the sensible material. Furthermore, while the God of the possibility proof is separate from the world, the God of the transcendental illusion is identical to the sensible world. Hence, it is not the case that the possibility proof is reincarnated in the form of the transcendental illusion in section two of the Ideal.

5. The Natural Course of Reason that Attempts to Prove God's Existence

Section three of the Ideal has received scant scholarly attention. The main reason may be that its function has been unclear. Indeed, it is not easy to see why section three is not somehow redundant. The title, ‘On the grounds of proof of speculative reason for inferring the existence of a highest being’ (A583/B611), may suggest that the section just introduces and pre-summarizes the refutations of the ontological, cosmological and physico-theological proofs to come. On the other hand, since it deals with a ‘natural course taken by every human reason’ (A584/B612; cf. A586/B614, A590/B618), one might think that the third section extends the natural illusion Kant discussed in section two.Footnote ⁴¹ But none of this holds. On my view, section three introduces an illusion that is different and independently motivated from the illusion in section two. For the latter attempts to establish a flawed idea of God, whereas the former provides a flawed ground of proof for taking the legitimate idea of God to correspond to an actually existing being. Therefore, it is only the illusion in section three that gives rise to the three attempts at proving the existence of the ens realissimum in the legitimate sense.

Kant distinguishes the two illusions as follows:

Kant does not consider the natural illusion in section two as a potential proof of God because, I take it, the idea of God as a sum total is self-contradictory; a proof based on this idea would be a non-starter. In section three, however, Kant discusses a ‘natural course’ of thinking that, if successful, would prove the existence of God in the legitimate sense. The natural course is a series of two illusions. It begins with ‘common experience’ and seeks for an ‘absolutely necessary being’ that grounds the conditioned beings in experience (A584/B612). Then, by a further step, we have the illusion that this being is the ens realissimum, which makes us conclude that the ‘being of the highest reality’ is the most plausible candidate for the absolutely necessary being (A586/B614).Footnote ⁴² Unsurprisingly, Kant thinks that this ‘natural’ way of proving the existence of God is mistaken (A587–8/B615–16), even though he credits it for having ‘a certain cogency’.

By contrast, some readers hold that the series of illusions in sections two and three are different steps of one extended argument. On their view, it is precisely the failure of the argument from section two to establish a legitimate concept of God which gives rise to another illusion.Footnote ⁴³ However, there seems to be a dilemma for their position. Either the natural course is just an extension of the preceding illusion in section two, but then we would still be committed to the illusion that God is the sum total of sensible realities.Footnote ⁴⁴ Or God is not the sum total of realities, but then it is unclear why the illusions are not independent from each other. The obvious solution for this dilemma is to accept that these illusions are separate.Footnote ⁴⁵

What makes the natural course of reason relevant for the rest of the Ideal is that Kant apparently builds the classification of the proofs of God's existence on it:

By speaking of ‘reason in gradually unfolding itself’, Kant plainly refers to the natural course of reason. The title of section three indicates that the section presents the ‘grounds of proof’ concerning the existence of God, which, in this context, means as much as a rough sketch of the argument(s).Footnote ⁴⁶ Arguably, the natural course of reason provides this ground of proof; and the three attempted proofs Kant aims to refute are motivated by the natural course.Footnote ⁴⁷ There is also an order in these proofs that corresponds to the natural course. For the physico-theological proof, which starts from experience, entails the cosmological proof, which in turn entails the ontological proof. Kant's argumentative strategy is to show that the ontological proof fails and then that the other proofs entail the ontological proof, so they fail, too (A606–7/B634–5, A625/B653, A629–30/B657–8).

The physico-theological proof strongly resembles the proof a posteriori from Beweisgrund. We find a ‘purposive order’ in the world that is:

Therefore, we conclude that there exists at least one being that possesses the great wisdom that is required to produce such an order. And because of the unity of this order there can only be one such being, namely God.Footnote ⁴⁹ We can summarize the beginning of Kant's reconstruction of the physico-theological proof as follows:

1. (1) The actual world displays an order that is only possible if there is a ‘wise cause’ (A625/B653) that grounds this order. Call this a ‘Wise Author’.

2. (2) There is at least one Wise Author.

3. (3) The unity of the world order reveals that there is only one Wise Author.

4. (4) There is exactly one Wise Author.

The physico-theological proof clearly corresponds to the natural course of reason: it begins by experience and seeks for an unconditioned ground of the order of nature. But so far the proof is incomplete: it has not yet shown that the Wise Author is an absolutely necessary being, let alone God. And Kant's refutation of the physico-theological proof is based on the claim that this gap cannot be bridged empirically.

Unfortunately, the structure of the refutation is not very clear. In any case, Kant seems to reject two different arguments that depend on two different ways of conceiving of the Wise Author. These ways correspond to what Beweisgrund considered the bad and the improved method of physico-theology, respectively. The first argument makes an ‘inference … from the analogy between natural products and those of human art’ (A626/B654). While Kant rejects this method, he holds that ‘once we are supposed to name a cause, we could not proceed more securely than by analogy with such purposive productions, which are the only ones where we are fully acquainted with the causes and the way they act’ (A626/B654). Yet this argument does not bring us very far. For it could:

Consequently, the proof ‘could at most establish an architect of the world, who would always be very limited by the suitability of the material on which he works, but not a creator of the world’ (A627/B655). A mere architect of the world could not be God because the architect has defects. In order to show that there is a creator, we have to prove ‘the contingency of matter itself’, and not only of the form in which nature is arranged (A627/B655). That matter is contingent means that it is dependent on a creator as its cause (A629/B657); and the Wise Author can only be God if he is the creator of matter, and hence of the world.Footnote ⁵⁰ We thus need to find a way that keeps the physico-theological proof empirical (as intended), but avoids the trap of the analogy with human artefacts.

For this reason, Kant goes on to discuss the second argument that he rejects, which ‘goes from the thoroughgoing order and purposiveness that is to be observed in the world, as a thoroughly contingent arrangement, to the existence of a cause proportioned to it’ (A627/B655).Footnote ⁵¹ This argument apparently makes empirical inferences from the harmony in substances (and their essences and laws). Unlike the first argument, it does not conceive of the Wise Author by analogy with human craftsmen. Still, Kant argues that the argument must provide us with the concept of a being that has ‘all perfection’ (A628/B656). But what we could get by this method at most is the existence of a being with ‘very great … power and excellence’ (A628/B656) – make the world as great as you want, we can always assume that its cause is just a very powerful finite being, not the infinite being that possesses all reality. Hence, the only way to save the physico-theological proof is by appealing to the cosmological proof (A629/B657), so the former must proceed as follows:

1. (5) The Wise Author is the creator of the world.

2. (6) The creator of the world is the absolutely necessary being.

3. (7) The absolutely necessary being is God.

4. (8) God exists.

Therefore, we have to account for propositions (5)–(7), which, if at all, could only be accomplished by the cosmological proof. As a result, the physico-theological proof entails the cosmological proof and is not independent of it. This is the key difference between the physico-theological proof and the proof a posteriori from Beweisgrund – the latter gave no account of why a unified principle of possibility requires the existence of God, whereas the former acknowledges that this can only be accounted for by the cosmological proof. Otherwise, the proof a posteriori and the physico-theological proof are closely related, as they attempt to prove God by relying on an improved method of physico-theology. Common to both is also Kant's criticism of them: there is always a gap in the inference from the actual world to the most real being.

I do not further follow Kant's refutations because the cosmological and even more the ontological proof are widely discussed and well-understood. What makes the physico-theological proof interesting in particular is that Kant attributes a positive role to it. For he says that the proof ‘enlivens the study of nature’ and offers a ‘guiding thread of a particular unity whose principle is outside nature’ (A623/B651). Kant discusses this positive function of the proof in the Appendix to the Transcendental Dialectic, to which we now turn.

6. The Regulative Function of the Transcendental Ideal

Despite the failure to prove God's existence, the transcendental ideal has an indispensable positive function for empirical cognition.Footnote ⁵² According to Kant, reason, in its real use, seeks for the unconditioned that is the condition of all conditioned beings; therefore, reason demands the existence of certain objects that are represented by ‘transcendental ideas’ (A334/B391). However, no adequate object can be given to transcendental ideas in experience – to this extent, reason is ‘dialectic’ and of no ‘constitutive’ use because reason cannot establish the existence of the unconditioned (A338ff./B396ff.). Notwithstanding this, there is a ‘regulative’ use of reason, as Kant argues in the Appendix to the Transcendental Dialectic. That is, the principles of reason do not establish the existence of an object in experience, but only direct the use of the understanding with regard to experience.Footnote ⁵³ The transcendental ideas have a positive and indispensable role for the regulative use of reason because they ground a necessary illusion (namely, that the unconditioned exists in experience) and, as it were, a focus imaginarius which reason seeks to approximate as far as possible (A644–5/B672–3).

This is a vast topic, and I will not elaborate on it further. But the idea that God grounds the order and harmony of the world is such a necessary illusion that is of regulative use for reason:

Apparently, the unity of experience is basically the same as the unity and harmony in essences that we are acquainted with from Beweisgrund. But now, Kant not only thinks that we cannot cognize the unity, but that it is even impossible that this unity can ever be realized in the world. Rather, the unity is an illusory task set by reason. For the ‘systematic complete unity’ of experience is an ‘idea’ (A677/B705); and since an idea is a non-empirical concept ‘which goes beyond the possibility of experience’ (A320/B377), the systematic unity ‘can never be presented adequately in experience’ (A677/B705).Footnote ⁵⁴ Therefore, it is only an (albeit necessary) illusion that God is the ground of the assumed unity.Footnote ⁵⁵

So Kant presents two transcendental illusions in the Ideal that must be well distinguished: first, an illusion that God exists as the sum total of sensible realities, second, an illusion that God exists as the ground of the unity of the sensible world. Both are motivated by an interest of reason: the former by the need for the all of sensible realities by virtue of the PTD, the latter by the need for a ground of unity by virtue of reason's interest in systematic unity. However, only the second illusion is of regulative use for reason.Footnote ⁵⁶