2.1 Obligation in Classical Theories of Natural Law

In the Natural Law tradition since Francisco Suarez and Hugo Grotius there is a broad consensus that all kinds of obligation derive in the final instance from a single source: from the divine will, from the reason-guided voluntas Dei: ‘Thy WILL be done in earth, as it is in heaven’. Accordingly, all obligations arising from human legislation must also be traceable to this single source: Fundamental natural law is ultimately divine law. Gottfried Achenwall, the author of the textbook Kant used for his lectures on Natural Law, can hardly be surpassed in clarity on this point:

Of course different legal scholars in that period attributed the law-giving authority of God to different qualities in God, whether it is that he does not allow contradiction because of his omnipotence (as in Hobbes – in reference specifically to legislation for the Commonwealth Ecclasiasticall), or that no reasonable doubt about his prescriptions is possible because of his omniscience and omnibenevolence (as in Leibniz), or that this authority simply derives from his privilege as creator of the world (as in Locke and Achenwall) – or (as for instance in Pufendorf) from some combination of these elements. But these are differences that have a common ground.

The unity of all kinds of obligation cannot arise from contingent properties of (human) nature or community, but requires a peculiar source. This is also indisputable for Immanuel Kant:

2.2 The Concept of Law

The Law (Jus), the natural law sensu stricto or simpliciter (see Achenwall, Prolegomena § 99), is essentially distinguished within general morality (i.e. natural law in the broader sense, late dictum/latius dicta) by the fact that it refers solely to those actions that (1) can be perceived through the external sense (‘sensu externo aliorum percipi possunt’), that is, also by other people and (2) on the other hand, constitute an injury to other people (a ‘violatio alteri homini’; see Achenwall §1 and § 112). Kant, of course, is familiar with the relevant discussion since Hugo Grotius’ time from Gottlieb Hufeland’s Versuch über den Grundsatz des Naturrechts of 1785 (which he reviewed immediately after its publication, see Rez Hufeland 8:127 ff.): only ‘external’ actions of this kind are both (1) capable of external (i.e. human) legislation (because only they are epistemically as well as practically accessible to other human beings) and (2) also in special need of it (because only they also affect other human beings). And these two aspects are also directly connected, as we already find in Grotius, who refers to the Christian tradition here. Briefly:

And within the framework of this tradition, the law of justice or of right, to emphasize this once again, is in the final instance also divine law.

2.3 Obligation in Kant

At the latest since his Grundlegung zur Metaphysik der Sitten of 1785, any kind of obligation for Kant is quite explicitly no longer dependent on the voluntas Dei endowed with punitive authority.Footnote ⁴ Any obligation is ultimately based solely on the pure legislative will (‘reiner Wille’, GMS 4:390) of the free being itself: Morality and autonomy are inseparable.

The formula for all varieties of obligation is thus the Categorical Imperative – or the one and only moral law, which in Kant has systematically taken the place of the one divine law:

There are no obligations, no duties without the moral law (period!). Since Kant also explicitly understands law or right as a relationship of persons (RL 6:230), and since personality for him is the ‘freedom of a rational being under moral laws’ (RL 6:223), the highest principle in respect of legal obligation must for him in the final instance be derived from the Categorical Imperative as the origin of any obligation, of all duties: alterum non datur;Footnote ⁸ and this is precisely what Kant succeeds in doing quite directly, as will be shown below.

2.4 The Principle of Right and the Principle of Morality

This derivation draws the formula of the General Law of Right directly from the formula of the Categorical Imperative, the supreme ‘principle of morality’. Here are the two formulas:

The derivation in question is of almost stenographic brevity and presumably therefore increasingly difficult to understand with greater distance from the natural law tradition. This has led to various elaborate strategies of reconstruction, up to the assumption that legal obligation is for Kant – contrary to the natural law tradition as well as contrary to Kant’s own explicit statements – not a special case of obligation (i.e. moral necessitation) through the Categorical Imperative at all, but a sui generis complex of ‘obligations’. The Doctrine of Right would thus – even against Kant’s architectural decision to include it in that very book – not be part of a Metaphysics of Morals at all,Footnote ¹¹ which nevertheless explicitly presupposes the doctrine of freedom from the Critique of Practical Reason:

The so-called independence thesis, which breaks up the systematic unity of the Doctrines of Right and of Virtue, must then consequently give its own answer to the question of what the binding nature of juridical laws, the obligation, is supposed to be based on (if not on the moral law), since no explicit answer to that question can be found in Kant’s texts. An additional hurdle here is that for Kant, obligation, as shown, is already a moral concept by definition, and this also refers, as we saw, directly to the theory of autonomy from the Groundwork and the second Critique.

If one starts with the above-mentioned, traditional definition of Jus (Recht) as a concept of external legislation (RL 6:229f.) and then adds the familiarFootnote ¹³ insight that there are actions or ways of acting that ‘cannot possibly be done with good intentions’ (fornication, adultery, drunkenness, blasphemy, and theft are the traditional standard examples), then one immediately will arrive at Kant’s formula in § C:

The part of the quotation after the dash (and starting with an ‘or’) might be irritating especially for readers who are too familiar with Kant’s moral philosophy as it is presented in the Groundwork and the Second Critique. There seems to be a problem in joining the concept of a maxim from his earlier writings to the formula in § C. In these earlier writings, there are no maxims of actions at all, but only maxims of the agents, these maxims being the subjective principles of their actions. And the moral worth of these actions depends on these subjective principles being in conformity with the Categorical Imperative.

But for Kant the individual subjective maxim or the intention of the agent cannot be recognized by other persons (and at least in some cases not even by the agent himself: GMS 4:407) and is thus, e suppositione, inaccessible to any external legislation (see § B, RL 6:230) – and thus this maxim cannot be the one that is meant here in § C. Why then does Kant add the phrase with the ‘maxim of the action’ and why does he add it with help of an ‘or’? The answer is straightforward: because Kant has to make sense of the expression that an action ‘can coexist with everyone’s freedom in accordance with a universal law’ in the framework of his own theory of action. How can an action be in conformity or in conflict with any law, if not by a maxim?

If an agent acts willingly at all (and does not merely behave unconsciously like a brute or even a plant), he acts according to some maxim (propositio maxima), that is, ‘according to the idea of laws, i.e. according to principles’ (GMS 4:412). And these principles are either compatible with the Categorical Imperative or they are not: Even the criminal is supposed to act on a maxim (RL 6:320n.) when he commits a crime. In short: Where there is no (subjective) principle, there is no (voluntary) action at all:

Only where there is a maxim, can there be a conflict with a rule or with a law. In the absence of any plausible alternative, the phrase ‘maxim of an action’ in fact has to be (and naturally can be) read as meaning that an action is right precisely if at least one (subjective) maxim can be conceived for this action that would be compatible with the Categorical Imperative (traditionally speaking: ‘for which there is some good intention’).

It is important to note that the externality of right (as defined in § A and then spelled out in § B) is the guiding idea here to transform (or to mitigate) Kant’s general moral commandment (his ‘Sittengesetz’) into his (mere) legal commandment (his ‘Rechtsgesetz’). In this step, Kant follows his point of reference Achenwall (see Section 2.2) seamlessly and without any attempt to distinguish his position from that of Achenwall. The maxim (or intention) according to which the agent actually acts cannot be judged in Jus, namely externally, ‘sensu externo aliorum’, e suppositione – and this is even mirrored in Kant’s definition:

And hence we read in a preliminary note to the Metaphysics of Morals:

1. 1. Doctrine of law. The concept of duties that take place independently of all incentives for their observation.

2. 2. The Doctrine of virtue is the epitome of duties that make themselves the incentive of movement.Footnote ¹⁷

Kant had already emphasized in the Groundwork (GMS 4:397) that in the case of the prudent merchant, for example, his clients cannot know what his maxim or his motive is, that is, whether he is acting only out of self-interest, merely ‘pflichtgemäß’, or whether he is acting out of duty (and whether his subjective maxim therefore has ‘moral content’, i.e. ‘value’). But – and this is the underlying thought, at least implicitly, and not only for Kant – if and only if no morally compatible maxim, that is, no maxim compatible with duty, can be conceived for an action in the given context, is it then definitely certain – even for an external legislation – that the agent is not acting according to such a maxim: simply because there is none. And if there is in fact no possible maxim at all compatible with the Categorical Imperative, the action itself (more precisely: the type of action as such) is therefore necessarily ‘pflichtwidrig’, morally forbidden: there is a duty to refrain.

On the other hand, if, for example, for any alleged act of ‘fornication or theft’, even one single subjective maxim could actually be conceived that is in accordance with the Categorical Imperative (i.e. if, traditionally speaking, ‘fornication or theft’ were also possible ‘with good intention’), then it would not be possible for any (external) human legislation to conceive of that particular act of fornication or theft itself as forbidden. For in order to recognize the unlawfulness of one’s action, one would have to know, besides the external action (or behaviour), that the particular subjective maxim of the person acting is not the one compatible with the Categorical Imperative. For this, however, one would need a ‘Herzenskündiger’ [‘heart’s discerner’] who ‘see[s] through the innermost part of everyone’s mind’ (KU 6:22 ff.) and in the given case actually recognizes the particular underlying subjective maxim of the agent and not only its ‘appearance’ in actions (ibid. 72; or RGV 6:99). Only then could we apply to it the standard of virtue (moralitas) over and above the standard of legal obligations (legalitas). Such an examination, at least according to the canonical view, only happens through God and, moreover, not ‘in time’:

Thus, by definition, law is only concerned with permitted (or prohibited) actions (legalitas), types of action for which a ‘pflichtgemäße’ maxim is possible (or not):

The value of a particular action – more precisely: the ‘moral content’ of the respective subjective maxim (GMS 4:398) of the agent – is the sole concern of ethics, because the subjective maxim of the agent, if there is any, is only accessible to the agent himself:

As far as I know, Kant never speaks of external actions that are in accordance with duty and that would themselves be possible exclusively from duty. And one should not even expect this, since in fact there is no ‘right’/‘just’ (external) action that one could not do for the ‘wrong’/‘evil’ reasons (while there are no ‘morally good’ pro tanto reasons for ‘unjust’ actions). In a given context, for every external action whose maxim has moral content one can easily imagine maxims that in fact do not have any such content. Think, for instance, of the prudent merchant with the subjective maxim, contrary to duty, of keeping contracts (if and) only if it benefits him. As long as he assumes that no breach of contract goes unpunished in the state, he will keep his contracts no less than the most virtuous merchant who always keeps them ‘from duty’. The ‘sensus externus aliorum’ will not be able to make out any relevant difference between the particular acts of the two – and will accordingly have to treat them the same in Ius. Kant expresses this with all the clarity one could expect:

And it is precisely for this reason that Kant can claim in the Friedensschrift (ZeF 8:366) that a republican state would also be possible for (‘für’, not ‘by’) a ‘people of devils’ (if they only had sense, reason, and demanded their preservation). Clever sanctioning institutions could turn even such Kantian ‘devils’ (like the strictly rational and selfish merchant just mentioned) into law-abiding ‘good citizens’ without having first transformed them into morally ‘good people’ – and, one can add: even without having to presuppose in them any ‘consciousness of obligation for the law’, namely pure practical reason, at all. This is what Kant pointedly wrote in 1795 for those German princes who wanted to justify their unwillingness to reform by saying that republicanism was suitable only for a nation of gods or angels (as Rousseau implicitly admitted).

Even more fundamentally (as we learn from the last quote), the positive value of an individual action (that it really ‘happened solely out of duty’), namely the moral content of its subjective maxim, not only remains hidden from legal-political authorities and fellow citizens, but, as Kant emphasizes here again, in the end it is not even reliably revealed to the agent himself (see RGV 6:20, TL 6:393, 441, 447). Therefore, a fortiori, all attempts to access the subjective maxims of the agent in the assessment of legalitas are at best a stopgap:

2.5 Persons and Things

But why then do we still need the status of a person, namely an awareness of the binding nature of moral laws in the Doctrine of Right, at all? The answer is evident if we take a broader point of view and recognize that the Doctrine of Right not only deals with the right to coerce but at the same time with limits of legitimate coercion vis-à-vis persons, vis-à-vis beings who can have duties and thus rights in the first place (see RL 6:239 note). § E of the Doctrine of Right leaves no question open here:

It is of course beyond question for Kant’s contemporaries and needs no further emphasis that one is allowed to treat any being (rational or not) at will as long as it does not have the status of a person, in Kant’s terms, as long as it lacks any awareness of obligation by the Categorical Imperative. In the Kantian sense these beings are mere things (‘Sachen’, RL 6:223) without duties and thus without rights. To treat such a ‘thing’ nonetheless like a person is not unjust at all.Footnote ²⁶ Hence the legal status of ‘personhood’ is mainly the privilege of being ‘right-bearers’. And often we can grant such a privilege even to beings who do not deserve it (or at least: to those of whom we do not knowFootnote ²⁷ whether they deserve it or not). This might be imprudent in a given case (to open the tiger’s cage), but it is no injustice to these beings. In sum, no rational being can complain if it is coerced by others to act according to the Kantian imperative of right:

This means: act in such a way that your subjective maxim could be one that would pass the test of the Categorical Imperative, even if the action in fact proceeds from fear of punishment (or even ‘from Avarice, or Lust, or Anger, or imprudent Pity, or Ambition, which are usually the Sources of the greatest Injuries’, see the quote from Grotius above). Persons as autonomous beings have no right to act against the Principle of Right in particular and thus have no moral reason to complain if they are coerced suitably – and non-persons have no rights at all and therefore no ‘moral’ reason to grumble if they are coerced.Footnote ²⁹

2.6 Right and Morals

If we reconstructFootnote ³⁰ Kant’s path from his ‘Principle of Morality’ to the ‘General Principle of Right’ in RL §§ A–E as proposed above it is short and completely transparent in substance – at least if we read it against the background of both the natural law tradition and Kant’s own doctrine of obligation. However, it is not necessarily easy for us later readers to follow. When we turn to the Doctrine of Right, after all, we usually have fewer preconceptions based on the teachings of the natural law tradition than on Kant’s writings in moral philosophy (such as the Groundwork and the Second Critique) with their dominant interest in the value of the actions and maxims. It can therefore easily appear to us as a shortcoming of Kant’s presentation that he (as it were entirely without preparation) speaks of an ‘action’ and ‘its maxim’, that is, of a ‘maxim of action’ sensu stricto (and not – as in the aforementioned writings – in the sense of a particular ‘maxim of the agent’ as an expression of his ‘Gesinnung’).

But then we overlook that two things seem to be self-evident for Kant – and should also be so for his readers: (1) Every action sensu stricto is performed under some maxim, for only in this way is it an expression of a will (or choice) which, as liberum arbitrium, determines itself not only according to stimuli (as the arbitrium brutum) but always also according to principles (A 802; GMS 4:412.26f.), be these conformable to morality or not. And (2): in Jus, the actual maxim of the agent (his or her subjective principle of action) must, by default, remain unknown and thus cannot play any role at all (thus it must not). Hence, the only thing that matters for the doctrine of right is (3) that an external behaviour in question (a) can be conceived as an action according to some maxim at all (and not merely as unreflective, as it were ‘brute’, behaviour). And if so, that this maxim can then also be thought of (b) as one which and under which the action ‘can coexist with everyone’s freedom according to a general law’. Then and only then is the external behaviour to be regarded as an external action (per ‘a’) and as morally permitted (per ‘b’), that is, as e definitione right. Thus others have a duty to refrain. All other behaviour may – this now almost goes without saying – be prevented by others with coercion anyway. They have no duty to refrain, since a person’s freedom is always already ‘restricted in the idea of it [sc. to lawful action]’ (§ C, RL 6:231). The obstruction of an obstacle to freedom, whatever else it may be, is at least not a restriction of freedom (§ D, RL 6:231) – and thus, for its part, cannot constitute a moral and thus, a fortiori, legal breach of duty:

By bringing into play his new concept of (moral) obligation, which he had precisely spelled out since the 1770s in terms of the Categorical Imperative – that is, by speaking not of the appropriate intention (intentio recta, animus bonus, etc.) of the agents but, more precisely, of their maxims and thus also about the possible maxims for the respective actions – Kant sharpens the distinction between Jus naturae and Theologia moralis already pointed out by Pufendorf in the Introduction of his De officio hominis et civis (1673).

We can also recognize that Kant already had precisely this separation of Jus and Ethica in mind for a long time, even if he first specified it definitively in his Introduction to the Doctrine of Right in 1797 with his new concept of ‘legislation’ (‘Gesetzgebung’, RL 6:218). He was able to be so brief in demarcating Ius from Ethica at that time because he could assume that everything that might be unfamiliar to his contemporary readers, namely his decisive philosophical innovations, had already been sufficiently dealt with in the Second Critique and in the Introduction to the Metaphysics of Morals, which explicitly (RL 6:222) precedes both parts, the Doctrine of Right and the Doctrine of Virtue. This was his new theory of the entia moralia, namely of personhood as autonomy, and thus of all laws of morality as categorical imperatives for maxims (RL 6:213f., 221ff.). And what was then still missing he summarized in the final definition of strict law (§ E), which I have already quoted (see Section 2.5).

2.7 Coercion in Natural Law

This also brought to an end the debate about the appropriate definition of Ius, which was widely documented in Hufeland’s book from 1785. For Kant the power of coercion is indeed analytically contained in the concept of Ius (thus RL 6:231 TL 6:396), but coercion need not therefore be a component of the definition of the concept of Ius/Right. The legal possibility of coercion is rather an immediate consequence of the externality of Ius – if we add the important insight that every external legislation for rational beings with sensibility requires some motive force in addition to the binding law in order to be able actually to determine actions (RL 6:222). Only in this way does a law become a component of a legislation (‘Gesetzgebung’). In the (merely external) Ius, only the threat of coercion in conformity with the law can serve as a motive force, since respect (‘Achtung’) for the law, which can fulfil this task in the (internal) Ethics, is reserved for the latter alone – and tertium non datur.

It was precisely the obvious requirement of a motive for bringing about humans’ compliance with the laws in Jus and Ethics that had led Wolff and the Wolffians to the wilfully exaggerated doctrine that obligation itself consisted essentially in a nexus of action and motivation, actio and motivum.Footnote ³² This doctrine was still followed by the young Gottfried Achenwall when, freshly appointed from Marburg to Göttingen, he published his first textbook on Natural Law in 1750 together with J. S. Pütter.Footnote ³³ In Göttingen, Achenwall was the successor of Samuel Treuer, who had already led a sharp polemic against Wolff’s doctrine of obligation in the 1730s and defended Pufendorf’s classical theistic doctrine against Wolff’s (and Leibniz’s) objections. In the year of Wolff’s death, Achenwall published a rehabilitation of Pufendorf’s theory of obligation fuelled by the writings of his predecessor.Footnote ³⁴ When he wrote the third edition of his textbook (and the Prolegomena) one year later he was no longer the Wolffian in the theory of obligation he had started out as in Halle and Marburg, but had turned into a Pufendorfian (see his Prolegomena § 50, quoted in Section 2.1) – and this is exactly how Kant then came to know him as the author of his textbook. Here legal obligation does not coincide with the effectiveness of the motive (provided, for example, by the threat of punishment), but stems from the authority of the will that links such a motive to the action. This is either the will of God as lawgiver, or of a human lawgiver authorized by divine natural law. Obligation is thus essentially a relationship of will and does not depend on the motive alone as in Wolff and in the early Achenwall but mainly on the authority of the law itself.

But even the later Achenwall still took for granted, that obligation presupposes that God’s lawgiving will makes the rules of reason obligatory by adding a motive (e.g. like the threat of punishment) to it:

In his lecture on natural law from 1784 Kant rebutted sharply even this ‘Achenwallian blend’ of Wolffianism and Pufendorfianism for the first time:

2.8 Kant’s New Concept of ‘Lawgiving’ (Gesetzgebung)

It took more than ten years until Kant could wrap this fundamental insight from 1784 into his new definition of a ‘Gesetzgebung’ (lawgiving), which puts together the ‘Gesetz’ (i.e. the source of obligation on one side) and the ‘Triebfeder’ (i.e. the source of motives on the other) into one new concept:

We know that we are obliged from the moral law alone whose binding force is a fact of reason (and the only ‘ratio cognoscendi’ of our freedom and personality, KpV 5:4, RL 6:239). And our motives to act in accordance with that moral law are twofold: the very idea of being obliged by one’s own reason itself (in ethical lawgiving by respect for the law) or something different (in juridical lawgiving by ‘praemia et poenas’). In the case of external actions, the latter may be even the threat of legal punishment by other human beings.

The unity of Jus and Ethica is guaranteed by the unity of the source of obligation alone: the one and only moral law. Their (only) difference lies in the source of motives for our acting in accordance with that law. These motives are thus not the grounds (or sources) of our obligation (pace Wolff) nor even necessary parts of it (pace Achenwall, Baumgarten – and the Canon of Kant’s First Critique). Since his Groundwork (1785) Kant thinks the other way round: motives are only morally possible, as long as they are in conformity with our duties from the moral law.

Therefore Kant’s terms ‘juridical duty’ and ‘ethical duty’ both refer to moral duties.Footnote ³⁸ The former refers to those kinds of moral duties that can be part of juridical lawgiving (see § A), the latter to those that cannot (RL 6:219). And since we can fulfil any duty from duty alone (since we are autonomous), all juridical duties are indirect-ethical duties when considered as part of ethical lawgiving (RL 6:221). ‘Pacta sunt servanda!’ is a juridical duty, but it does not cease to oblige us if the threat of enforcement or punishment is actually missing (RL 6:219).

Indeed, we find the core of the classical natural law doctrine in Kant’s Introduction to the Metaphysics of Morals – but, of course, without the heteronomistic reference to the Will of God, and without any reference to motives:

Accordingly, a central task of the main text of the Doctrine of Right will be to demonstrate our obligation (as persons) to submit to an external legislation that represents the idea of a general legislative will of the people (Rousseau’s volonté générale): Thus we will impose new juridical duties on ourselves as persons. The first step of that demonstration essentially takes place in §§ 1–9 of Private Right, where Kant shows that any juridical reference of persons to external objects (‘Äußeres Mein und Dein’), in particular to the finite land supply of the earth, the ‘globus terraquaeus’ (RL 6:352), can only coexist with the freedom (see § C, RL 6:230) of those persons through an omnilateral contract, namely through establishing a common will of all those concerned as an artificialFootnote ⁴⁰ source of their obligations (§§ 8f., RL 6:255ff.). Hence the moral imperative to establish public right, according to Kant its categorical imperative, is: exeundum est e statu naturali (RL 6:307). And since this (moral) duty ‘allows for an incentive other than the idea of duty’ it is a juridical duty – and thus, of course, an indirect-ethical duty too (RL 6:219).

2.9 Epilogue

Returning to the core idea of our reconstruction of the argument in §§ A–E of the Doctrine of Right, I would like to point out that (to paraphrase a formulation of the Groundwork, GMS 4:454) ‘the practical use of common legal reasoning confirms the correctness of Kant’s deduction of the general principle of Right’. Those who convince the court, for example, that their conduct can be interpreted as an expression of acting according to a permissible maxim are usually acquitted – albeit often grudgingly: think, for example, of major economic offences, when it is said, mutatis mutandis, ‘An intention to defraud could not be proved’.

Some external conduct, on the other hand, can only be declared an attributable act by assuming such an ‘intention to defraud’ – and as such would then definitely be unjust. Of course, it is always a question of the extent to which the external conduct (including the previous history and the expected course of action) can and must be taken into account in this consideration. But let us take as an example someone who in a department store carefully stows a tiny umbrella in his bag and immediately rushes out into the sun-drenched pedestrian zone without paying and disappears into the crowd. He will not be able to explain convincingly to the store detective who has rushed over (and later to a judge) that he only wanted to try out the umbrella once in order to bring about the decision to buy it.Footnote ⁴¹ But if he somehow managed to explain his behaviour convincingly as being compatible with another ‘legal’ maxim formerly undisclosed, for the court his behaviour would count only as the misleading expression of an essentially lawful action, according to whose maxim his freedom may well coexist with that of others (perhaps a ‘mere fault’, not a serious crime; RL 6:224). And because not only the judge, but also any possible lawyer, is not a ‘heart’s discerner’ and therefore can at best assume the maxim, it is in principle morally possible for the lawyer to plead before the judge for the acceptance of that possible maxim, according to which the conduct of his client does deserve the least drastic punishment or no punishment at all: In dubio pro reo.