1.2 Three Supreme Principles

According to the Metaphysics of Morals, Morals, Right, and Ethics each has its own supreme principle. In what follows, we will approach the question of how Right relates to Morals and Ethics by looking at the relation between their supreme principles.

In the Introduction to the Metaphysics of Morals, Kant writes: ‘The supreme principle of the doctrine of morals (Sittenlehre) thus is: act on a maxim that at the same time can hold as universal law’ (MS 6:226) – a principle that, one page prior, he calls the ‘categorical imperative, which as such only affirms what obligation is’ (MS 6:225). While a maxim is a principle followed by an individual agent (for some purpose, and given the right circumstances), a universal law consists in everyone’s acting on a particular maxim (see e.g. GMS 4:400n; GMS 4:420n; KpV 5:19). Thus, a maxim can hold as universal law if it is possible (in some suitable sense of ‘possibility’) for everyone to act on it. Let us call maxims that can hold as universal laws ‘universalizable’. Thus, the SPM requires us to act on universalizable maxims.

In the Introduction to the Doctrine of Virtue, which presents his account of Ethics, Kant claims that the ‘supreme principle of the Doctrine of Virtue is: act on a maxim of ends the having of which can be a universal law for everyone’ (TL 6:395). Kant does not explain what he means by a ‘maxim of ends’, but the ends in question are presumably the two ‘ends that at the same time are duties’, namely one’s own moral perfection and the happiness of others (TL 6:385; cf. TL 6:391–94). So the supreme principle of Ethics (SPE) can be understood as requiring us to act on universalizable maxims that are suitably related to these two ends (e.g. to act on a maxim of beneficence to promote the happiness of others).

While Kant does not explicitly state a ‘supreme principle of the Doctrine of Right’, it seems that the ‘universal principle of Right’ (UPR) has exactly that function. It reads: ‘Any action is rightful that is such that, or in accordance with its maxim, the freedom of choice of each can coexist with everyone’s freedom in accordance with a universal law’ (RL 6:230).Footnote ¹⁰ One page later, Kant formulates a ‘universal law of Right’ (ULR), which I take to be substantially the same principle as UPR but that brings out the parallel with the other two ‘supreme principles’ even more clearly: ‘act externally such that the free use of your choice can coexist with everyone’s freedom in accordance with a universal law’ (RL 6:231). Since UPR (in the German original) is not grammatically well formedFootnote ¹¹ and is thus more difficult to interpret, while ULR is formulated in a way that is parallel to SPM and SPE, I will concentrate mainly on ULR. ULR requires us to act ‘externally’ (that is, irrespective of one’s motivation) in such a way that one’s own free acts (‘free use of your choice’) ‘can coexist’ with those of others ‘in accordance with a universal law’. If we read ‘coexist’ as ‘being jointly realized’ and ‘in accordance with a universal law’ as ‘affecting everyone in the same way’, we can paraphrase ULR as follows: restrict your exercise of free agency in such a way that your acts do not prevent others from exercising their free agency in the same way.

In sum, Kant formulates three ‘supreme principles’, one for Morals (SPM), one for Ethics (SPE), and one for Right (UPR/ULR). Each of these three principles invokes the idea of universal law: in fact, this idea seems to be the only element common to all three principles. (SPM, SPE, and ULR are also all formulated as imperatives, while UPR is not.) Only SPM and SPE require that one’s maxim be able to be (or to hold as) a universal law; by contrast, ULR does not even mention one’s maxim and only requires that one’s freedom be able to coexist with the freedom of others in accordance with a universal law. (UPR does mention a maxim but does not require that it be able to hold as a universal law.) Before we look at the difference between SPM and ULR more closely, let us first turn to the relation between SPM and a fourth principle, namely the Categorical Imperative we know from the Groundwork.Footnote ¹²

1.3 Is SPM Identical with the Categorical Imperative Introduced in the Groundwork?

In the Groundwork, Kant offers (at least) four different formulations of the Categorical Imperative (cf. GMS 4:436), all of which are meant to be expressions of the same ‘supreme principle of morality’ (GMS 4:440; cf. GMS 4:392). The most general and fundamental of these formulations, and the one closest in wording to SPM, is FUL. It reads:

For a maxim to become a universal law, I take it, is for it to hold as a universal law on which everyone acts. To will through one’s maxim that one’s maxim become a universal law is to want the conjunction of two things, namely that one acts on that maxim and that everyone else does the same. FUL thus prescribes a two-step procedure: (i) imagine that everyone acts on one’s maxim and (ii) ask whether one can rationally want both that one acts on that maxim oneself and that everyone else acts on that maxim. If the result of step (i) is that this is logically impossible, or if the result of step (ii) is that you cannot rationally want this (GMS 4:424), then the action is prohibited, and otherwise it is permitted.

Now compare FUL with SPM, which says: ‘act on a maxim that at the same time can hold as universal law’ (MS 6:226). SPM and FUL are similar in various respects; most importantly, both require us to act on universalizable maxims. But there is at least one important difference: while FUL requires that one be able to ‘will’ that one’s maxim become a universal law, SPM only requires that the maxim be able to ‘hold’ as a universal law. Apparently, the second step required by FUL has fallen away in SPM. In order to determine what is required by SPM, all one needs to do is ask whether it is possible for everyone to act on one’s maxim.

What is the significance of this difference? In the Groundwork, Kant identifies the duties that emerge from the first step of FUL (based on a ‘contradiction in conception’) with narrow or strict duties and those that emerge from the second step (based on a ‘contradiction in willing’) with wide or meritorious duties (GMS 4:424). Does this mean that SPM is only a principle of narrow and not of wide duties? This is unlikely, since SPM is supposed to be the fundamental principle of the Metaphysics of Morals, which includes both narrow duties (which Kant now tends to identify with juridical duties) and wide duties (which are ethical duties).Footnote ¹³

Could it be that the difference between FUL and SPM does not have any significance at all because Kant is simply expressing the same thing in the different formulations? This also seems unlikely. First, the idea of ‘willing one’s maxim (at the same time) to be a universal law’ is so prominent in the Groundwork that it can hardly be a coincidence that Kant deleted it from the formulation of the SPM.Footnote ¹⁴ Second, in the Metaphysics of Morals, the idea that the Categorical Imperative provides a test procedure for determining our duties recedes into the background and is replaced by a catalogue of juridical rights and ethical virtues.Footnote ¹⁵ It seems plausible that this change (whether substantial or merely expository) is reflected in the formulation of SPM.

In any case, we cannot straightforwardly identify SPM with FUL. Whatever the reason for Kant’s dropping of the reference to ‘willing through one’s maxim’, the two principles differ in subtle ways that presumably reflect the different roles they play in the Groundwork and in the Metaphysics of Morals.Footnote ¹⁶ And this means that we cannot simply identify the principle that covers both Right and Ethics as parts of Kant’s conception of Morals with the fundamental principle of Kantian Morality as defined in the Groundwork.

I think that the difference between SPM and FUL goes even further than indicated thus far, however. As the architecture of the Metaphysics of Morals demands, SPM is supposed to hold for both Right and Ethics. But how can that be? As we saw, ULR in effect requires us not to act in ways that prevent others from doing what they have a right to do, where our rights and theirs are allocated ‘in accordance with universal law’, that is, in the same way for all. But on Kant’s own account, not infringing on other people’s rights is something one can do while acting on a maxim that is not universalizable. For instance, Kant claims that lying as such (unless under oath, in a contract, etc.) does not infringe on other people’s juridical rights, since it is up to them to believe us or not (RL 6:238). But clearly, the maxim of lying whenever it is convenient is not universalizable, according to Kant (GMS 4:403). Similarly, Kantian Right permits us not to cultivate our talents and abilities, while Kantian Ethics requires this (TL 6:392; cf. GMS 4:422–23). The list of acts and maxims that are juridically permitted according to ULR but not universalizable could easily be extended.Footnote ¹⁷ So the problem is this: if SPM requires us to act on universalizable maxims but the supreme principle of Right, ULR, does not require this, how can SPM also hold for Right ? or conversely, how can ULR fall under SPM as a special case?

We will return to this question soon. For now I want to suggest that we can see how SPM can cover both Right and Ethics if it is understood, despite its imperatival form, as giving expression to (nothing more than) the following twofold claim: (i) there are moral rights and obligations (ii) that are the same for all rational beings. While the imperatival form of SPM can be taken to give indirect expression to (i), the idea of moral universality (ii) is contained in the expression ‘universal law’. As Kant himself points out, SPM ‘only affirms what obligation is’ (MS 6:225). SPM requires us to act on maxims that can be universal laws. But if a maxim can be a universal law, then it is a universal law in the sense that everyone is at least permitted to act on it. Conversely, if my maxim cannot be a universal law, then everyone else is prohibited from acting on it too. Thus, according to SPM, acting on some maxim is morally permitted (prohibited) for one person if and only if it is morally permitted (prohibited) for everyone else. This means that SPM in effect ‘affirms what obligation is’ on a formal level by saying that rights and obligations, whether juridical or ethical, must be the same for all. It thus gives expression to the idea of moral universality.

Only if read in this minimal way can SPM serve as the supreme principle of both Ethics and Right. Put differently, what is common to Right and Ethics is not the command to act only on universalizable maxims (because that command, according to Kant, does not hold for Right), but rather the idea that there are moral rights and duties and that they take the form of ‘universal law’, which means that what is permitted (prohibited) for one must be permitted (prohibited) for all. Note that implicit in SPM and the idea of moral universality is the idea of moral autonomy. If moral rights and obligations must be the same for all rational beings, this is because they are based only on what all rational beings as such share, namely the capacity of (pure practical) reason. But this means that we can understand these rights and obligations not as external requirements but as an expression of our own will insofar as it is rational.

There are two things I would like to take away from our discussion of the relation between SPM and FUL. First, SPM and FUL are distinct principles in that only FUL, but not SPM, requires us to act only on maxims we can will to be universal laws. Thus, the supreme principle of the Metaphysics of Morals is not identical with (the basic formulation of) the supreme principle of morality Kant introduces in the Groundwork. Second, despite its imperatival form, SPM should be read as claiming that there are moral rights and obligations that, because they are based on pure practical reason, are the same for all rational beings. Only if read in this minimal way can SPM serve as the fundamental principle of both Right and Ethics.

1.4 Why ULR Cannot Be Derived from the Categorical Imperative Alone

According to a widespread reading of the Introduction to the Doctrine of Right, ULR can be derived from FUL (or at least falls under FUL as a special case). On this reading, the three features of Right that Kant mentions in RL §B (externality, efficaciousness, and formality) and that take him to his definition of Right and to UPL/ULR (RL 6:230–31) restrict FUL to the ‘formal’ compatibility of ‘external’ actions insofar as they can affect others. Since ULR requires me to restrict my sphere of external agency to the conditions under which it is formally compatible with the same sphere’s being granted to everyone else (‘in accordance with a universal law’), ULR may thus seem to be a restricted version of FUL.

But this picture cannot be correct. First, note that Kant himself never explicitly claims that ULR, UPR, or his conception of Right can be derived from FUL (or from any other version of the Categorical Imperative or from Kantian Morality more generally). He only says that Right is one of two branches of Morals, under which it falls or can be subsumed. Second, FUL commands us to act only on maxims we can will as universal laws. But as we have just seen, ULR in no way requires us to act on maxims that qualify as universal laws. All it says is that our actions (UPR: and their maxims) should be compatible (in a specific respect) with everyone else’s actions in accordance with a universal law. Thus, the appeal to universal law serves to qualify the way in which one’s actions and maxims are to be made compatible with everyone else’s, not to characterize the quality of one’s maxim. But if FUL requires us to act on universalizable maxims while ULR does not, ULR cannot be a special case of FUL (in the sense in which, say, ‘Do not lie under oath’ is a special case of ‘Do not lie’). And if it is not a special case of FUL, then it cannot be derived merely by restricting FUL to a specific set of actions or conditions.

Against this, one might respond that for ULR to be a restricted case of FUL it is not necessary for all acts permitted by ULR to be permitted by FUL. Since ULR only concerns external acts, irrespective of whether their motive is duty, lying, for instance, might well be permitted by ULR and prohibited by FUL, even if ULR is derived from FUL by restriction to external acts. Lying as such, except under oath, etc., is simply not an action type that falls under ULR.Footnote ¹⁸

While this is correct as far as it goes, it does not show how ULR can be derived as a special case of FUL. The problem is not simply that there are acts that are permitted by ULR but prohibited by SPM. Rather, the reason why something is permitted or prohibited according to ULR differs from the reason it is permitted or prohibited according to FUL. In the case of FUL, an act is permitted because its maxim is universalizable. In the case of ULR, an act is permitted not because its maxim is universalizable (since there are permissible acts whose maxim is not) but because it can coexist with everyone’s external freedom in accordance with universal laws. If ULR were just a special, restricted case of FUL, one would expect the reason why something is permitted (or prohibited) to be the same for both principles (or at least that the reason in the more general case forms part of the reason in the more specific case). But that is not so. Rather, FUL and ULR impose substantially different normative requirements on us (act on universalizable maxims; respect the equal freedom of others). Given the substantial differences between FUL and ULR, it seems unlikely that there is any other way to derive ULR directly from FUL or any other version of the Categorical Imperative.

Against this conclusion, Paul Guyer has proposed not one but three ways in which ULR (or rather UPR, which is the principle on which Guyer focuses) can be derived from the Categorical Imperative without additional normative input.Footnote ¹⁹ First, according to Guyer, the most fundamental value that grounds Kant’s ethics is the value of freedom, and its most fundamental principle is thus to act in such a way that the ‘greatest use of freedom is possible’.Footnote ²⁰ UPR is then supposed to follow ‘from application of the idea of the “greatest use of freedom” to the interpersonal case’.Footnote ²¹ Second, Guyer asks whether the ‘maxim of arrogating as much freedom for themselves as they like regardless of the effect on the freedom of others’ is universalizable (according to him, it is not).Footnote ²² Third, UPR ‘can also be derived from the Formula of Humanity’ (FH), which on Guyer’s reading requires that I ‘exercise my own capacity to set ends only in ways consistent with the capacity of all others to set ends’, from which it presumably follows that ‘the formula of humanity tells me always to exercise my freedom of choice only in ways that leave others equal freedom of choice – precisely what is required by the Universal Principle of Right’.Footnote ²³

I think that the first derivation fails because it does not distinguish between two notions of external freedom at issue in Kant’s conception of Right: one’s ‘pre-juridical’ freedom of choice and one’s juridical freedom (the latter being both limited and protected by universal laws of Right).Footnote ²⁴ Clearly, it cannot be a fundamental moral principle to secure the ‘greatest use of freedom’ if by that we mean the unrestricted use of one’s freedom of choice, since this would include unrightful and immoral uses of freedom. But if the principle is restricted to juridical freedom, it just becomes a version of UPR: secure the greatest possible freedom for yourself that is compatible with the same freedom for everyone else. UPR would then be derived not from FUL but from a principle that is just another version of UPR and that, therefore, cannot be the supreme principle of both Right and Ethics. Perhaps there is some third notion of external freedom (let us call it moral freedom) that is fitting for a moral (not specifically juridical) principle of greatest freedom – perhaps ‘freedom as constrained by FUL’. But if so, Guyer does not provide it here.Footnote ²⁵

The second derivation rests on the claim that the maxim of arrogating more freedom for oneself than one grants to others is not universalizable. Bringing this idea even closer to a possible derivation of ULR or UPR, we can ask whether the maxim of not (always) acting in accordance with ULR (that is, not always ‘act[ing] externally such that the free use of your choice can coexist with everyone’s freedom in accordance with a universal law’) passes the FUL test. Obviously, it is logically possible for this maxim to be a universal law, since such a situation is just what Kant, with the tradition, calls ‘the state of nature’ (natürlicher Zustand, RL 6:306). Now according to FUL, we must next ask whether one can rationally will such a situation, and Kant is ultimately committed to the claim that one cannot (cf. RL 6:307).

But note that his argument for this claim is that only in a civil state (bürgerlicher Zustand, a state in which Right is realized) can people’s juridical rights be secured and conflicts about such rights resolved in a non-arbitrary way (namely in court) (RL 6:306). Thus, Kant’s argument against the state of nature already presupposes what he calls ‘private Right’ (with its presumptive subjective rights, e.g. to freedom of speech and to property) and thus presupposes UPR. Moreover, Kant claims that in the state of nature ‘no one is bound to refrain from encroaching on what another possesses if the other gives him no equal assurance that he will observe the same restraint toward him’. He concludes:

Thus, Kant himself argues that, at least from the perspective of the individual agent, willing to live in the state of nature is rationally possible (‘as if by mutual consent’) as long as we ignore each other’s juridical rights. It is only once we take into account the additional requirement to leave the state of nature, which already presupposes private Right and ULR, that this maxim can no longer be willed as universal law. But this means that the maxim in question (of not always acting in accordance with ULR) fails to be universalizable only if we already presuppose that there are juridical rights according to ULR, which is just what was meant to be derived.

Finally, we can see that something is amiss with Guyer’s third derivation from the fact that its conclusion (‘to exercise my freedom of choice only in ways that leave others equal freedom of choice’) contains an idea not contained in FH as interpreted by Guyer (‘exercise my own capacity to set ends only in ways consistent with the capacity of all others to set ends’), namely that of ‘equal freedom’. FH requires me always to treat others in ways to which they can rationally consent. But in not respecting their juridical rights (not granting them equal freedom), I do not necessarily violate this requirement. The reason, again, is that in the state of nature, as long as others do not grant equal freedom to me, I am not morally required to grant equal freedom to them. Thus, it is not the case that in the state of nature, where there is no ‘equal freedom’ because, ‘as if by mutual consent’, the strongest prevails, I automatically violate FH (treat others as mere means), since our relation may still be entirely reciprocal and consensual.

I conclude that Guyer’s three proposed derivations of UPR/ULR from FUL and FH are unsuccessful. Ultimately, I think that no such derivation is possible because Kantian Right is not a state in which everyone voluntarily acts in accordance with ULR (that is, respects equal spheres of freedom for all), but rather a state in which everyone is guaranteed to act that way, willingly or unwillingly, where this guarantee involves the use of coercion where necessary. As I have argued elsewhere, this ‘authorization to use coercion’, which according to Kant is analytically linked to the concept of Right (RL 6:231), cannot be justified merely by appeal to FUL, FH, or SPM.Footnote ²⁶ Let me close this section by briefly commenting on Guyer’s discussion of one of my arguments for this claim.Footnote ²⁷

The argument in question is that if FUL were to include the authority to use coercion in the juridical case, it would also include that authority for some ethical cases, which would clearly be inappropriate. Guyer thinks that ‘this is the most promising’ of the arguments I offer and rightly points out that the ‘difficult cases’ for someone who wants to resist this argument ‘will be perfect duties to others, such as simply keeping promises, that do not seem to be desirable candidates for coercive enforcement’.Footnote ²⁸ Guyer’s main line of response is that failure to keep non-contractual promises is ‘not really a hindrance to freedom’ and that therefore the keeping of such promises cannot be coercively enforced. So the idea is that while we are morally obligated to keep our non-juridical promises, this obligation cannot be coercively enforced because breaking such a promise does not hinder the promisee’s freedom. Guyer admits that this ‘may seem implausible’, but he then argues that ‘rational agents do not place too much weight on promises that do not take the form of legally enforceable contracts’.Footnote ²⁹ Therefore, according to Guyer, their freedom is not hindered by someone’s breaking such a promise. But that still seems implausible. We often rely on promises that are not legally enforceable, such as a friend’s promise to stand by my side even in difficult times or a wedding vow of mutual faithfulness. In many ways, non-juridical promises can be more important to us than legally binding contracts, and important parts of our lives depend on them. Moreover, breaking a non-juridical promise can very well limit our freedom in that it can hinder us from doing something we could, and would, otherwise have done. Thus, we still lack a principled way to distinguish between duties that are coercively enforceable and those that are not without already presupposing a Kantian conception of Right (with its analytic link to coercion).Footnote ³⁰

In sum, there is reason to doubt that ULR can be derived from FUL alone (or from any other version of the Categorical Imperative) without introducing additional normative resources, and recent attempts to provide such a derivation remain unconvincing.

1.5 How ULR Can Be Derived from SPM (in Conjunction with the Idea of Subjective Rights)

In this section, I will argue that ULR (and thus Kant’s conception of Right) can be understood as combining SPM with the claim that there are coercible juridical rights. If there are such rights, then, according to Kant, it follows analytically that they must form a system, which Kant calls Right. (Note that the following ‘derivation’ of ULR does not in itself constitute a justification of juridical coercion but presupposes that there are coercible juridical rights. I will return to the question of how to justify coercion at the end of this chapter.)

Let us start from the claim that juridical rights must form a system. This follows from a principle I have elsewhere called the Impossibility of Conflicting Juridical Rights (ICJR).Footnote ³¹ It says that if you have the right to do F, then no one else can have a right to do something that makes it impossible for you to do F:

Thus, ICJR implies that all juridical rights must be compossible, that is, that it must be possible for all juridical rights to be jointly exercised. In recent legal and political theory, this claim has been the subject of much debate.Footnote ³² Nevertheless, I take ICJR to be a conceptual truth about juridical rights in Kant’s sense. To be sure, there can be ‘rights’ in a wider sense that do conflict – such as my ‘right’ to privacy and your ‘right’ to security. But these are not all-things-considered juridical rights in the Kantian sense, which are coercively enforceable, but rather pro tanto rights (or perhaps, in analogy with Kant’s resolution of conflicting duties, grounds of rights; cf. MS 6:224). Only when it has been determined (typically by a court of law) whether in a particular case your ‘right’ to security or my ‘right’ to privacy prevails do we have a juridical right in Kant’s sense that can be coercively enforced (e.g. my right to keep my email messages private or your right to have them searched). Even though Kant does not explicitly articulate ICJR, he is clearly committed to it by the way he argues for the analytic link between right and coercion (RL 6:231).Footnote ³³

Now, ICJR implies that different people’s spheres of legally protected freedom (subjective juridical rights) must be limited in a way that avoids the possibility of conflicting rights. If A has an unrestricted right freely to speak her mind and B has an unrestricted right not to be spoken ill of in public, these rights can conflict if A thinks ill of B and makes use of her right to say so publicly. Thus, because of ICJR, either A’s or B’s right must be limited in order to form a system of compossible rights. In principle, this can be done in many possible ways, for example by giving all rights to one person and none to all others, or many rights to women and few to men. Any distribution of juridical rights that avoids conflicts between rights would satisfy ICJR. But clearly, unequal distributions of rights violate the idea of moral universality expressed in SPM, which requires that juridical rights (spheres of legal freedom) must be the same for all.

But if ICJR is combined with SPM, what results is the idea of Kantian Right and ULR. While ICJR implies that spheres of freedom must be limited (or ‘united’) so as not to conflict, SPM means that this limitation must be the same for all (‘in accordance with universal law’). Taken together, they require us to limit people’s spheres of freedom in a way that grants everyone a sphere of juridically protected freedom that is compatible with granting the same sphere of freedom to everyone else. Thus, given the idea of moral universality, if there are any juridical rights at all, they must conform to ULR. Assuming that there can be no justification of Kantian Right (with its emphasis on ‘universal law’) that does not appeal to the idea of moral universality, this means that SPM is necessary, and in conjunction with ICJR also sufficient, for justifying ULR.Footnote ³⁴

I hope that the reading developed here can capture what I take to be the correct insight in interpretations of Kantian Right that aim to derive ULR or UPR from FUL or SPM, namely that Kantian Right is one instantiation of a more general idea that is also instantiated, although in a different way, in Ethics. What is common to Right and Ethics is the assumption that there are moral rights and obligations which, because they arise from rational principles, are the same for all rational beings, a universality which is expressed in SPM (as well as in ULR and SPE) by appeal to ‘universal law’. Where the reading proposed here differs from those other readings, however, is in its denial that either FUL or SPM alone is sufficient to justify Kantian Right. On the reading suggested here, what is needed in addition to SPM (i.e. in addition to the idea of moral universality) in order to justify Kantian Right is the assumption that there are coercively enforceable rights. While Right applies the idea of moral universality to subjective juridical rights (requiring that the coexistence of individuals’ rights results in equal rights for everyone), Ethics applies it to people’s maxims and ends (requiring us to act only on universalizable maxims).

1.6 The Resulting Picture

In this chapter, I have tried to elucidate the relation between Kantian Morals, Right, and Ethics by discussing the relation between their ‘supreme principles’ (and the Categorical Imperative from the Groundwork). The basic principle of Kantian Morals is SPM, which Kant formulates as the imperative to act on maxims that can hold as universal laws. As I have argued, however, SPM is best understood as an expression of the claim that there are moral rights and obligations which, because they arise from pure practical reason, are the same for all rational beings.

This general claim has two basic applications: Right and Ethics. In Right, the idea of moral universality is applied to juridical rights. Since the juridical rights of different people cannot conflict, they must be (coercively) ‘united’ in a system of rights. SPM requires that these rights be distributed equally, ‘in accordance with a universal law’. In this sense, Right is a special case of Morals, and its supreme principle (UPR/ULR) is a special case of SPM. But this does not mean that ULR can be derived from SPM alone. What can be derived from SPM in conjunction with the idea of juridical rights is the conditional claim that if there are juridical (coercible) rights, they must take the form of a system of equal rights for all. In order to derive UPR/ULR itself, the existence of juridical rights must already be presupposed. But note that this does not mean that juridical rights are normatively prior to, or more basic in the order of justification than, UPR/ULR. It only means that we can understand UPR/ULR as a combination of central elements of Kantian Morality (rights and obligations based on pure practical reason, moral universality) and the idea of enforceable rights (which necessarily form a system). When it comes to justifying UPR/ULR or to explaining its normative validity, there is nothing more basic on which UPR/ULR could be grounded, because the fundamental juridical rights that are normatively valid for us, according to Kant, are those that hold equally for all rational beings, that is, those defined by UPR/ULR.

In Ethics, the idea of moral universality is applied to the two ends reason prescribes to each of us: moral self-perfection and the happiness of others. As Kant maintains, these ends must be pursued only in ways that respect the equal moral standing of all, which means that they must be pursued in maxims that can hold as universal laws (SPE). Even though this has not been the topic of this chapter, there is little reason to assume that SPE, so understood, can be derived from SPM alone. For instance, that the happiness of others is ethically important is something that does not follow from the idea of moral universality (SPM). Rather, the two ethical ends must be presupposed, and combined with the idea of moral universality, in order to arrive at SPE. Again, this does not mean that self-perfection and the happiness of others are normatively more fundamental than SPE, but only that SPE can be understood as a combination of these two ends with other elements of Kantian Morality. When it comes to justifying SPE, there is nothing more basic to which one could appeal and that would explain the validity of SPE without already presupposing SPE in one way or another.

Thus, Kant’s conception of Morals is united by the ideas (i) of rights and obligations based on reason and (ii) of ‘universal law’ or moral universality. It is these ideas that are shared by both Right and Ethics. As I have argued, however, this does not mean that the supreme principles of Right and Ethics can be derived from something more fundamental (such as SPM or FUL). On the reading defended here, Right and Ethics are both equally fundamental and underivable expressions of Kantian Morals, with its idea of moral universality.

Now it may seem that, unlike Ethics, Right stands in need of further rational justification because it involves the authorization to use coercion. Since coercion consists in making people do something they would not have done freely (cf. RL 6:231; TL 6:379), we need to explain what gives us the right to coerce someone and thus to restrict their freedom. But note that if Right cannot be derived from anything more fundamental, this does not mean that it cannot be rationally justified from within the perspective of Right. The inherent rationality of Right (including the authorization to use coercion) is evident in the fact that someone who violates other people’s rights cannot reasonably complain if she is coerced into respecting those rights (as long as the coercive measures are proportionate, of course).Footnote ³⁵ In particular, she cannot rationally insist on her right to do as she pleases, or her right not to be coerced, since juridical rights, as we have seen, necessarily form a system in the sense that one person’s right is mutually dependent on any other person’s right. (This is implied by ICJR.) It is therefore rationally impossible to insist on one’s own rights without granting equal rights to everyone else. (This is implied by ICJR in conjunction with SPM.) Thus, while it may be rationally possible to reject the whole idea of Kantian Right, it is impossible to rationally object to the fact that other people protect their own rights and the rights of others coercively, since doing so would amount to insisting on one’s own right not to be coerced, which in turn implies granting equal rights to all others. This, it seems to me, is entirely sufficient as a normative justification of Kantian Right.