Book Review: Byrd & Hruschka’s Kant’s Doctrine of Right

Kant’s Doctrine of Right: A Commentary by B. Sharon Byrd and Joachim Hruschka, Cambridge University Press, 2010.

B. Sharon Byrd and Joachim Hruschka bill their new book on Kant’s legal philosophy as a commentary but it is really much more than that. It is an authoritative and comprehensive systematization of Kant’s legal philosophy. What makes it a commentary is that the authors deal with all of the central ideas in Kant’s Doctrine of Right rather than just selecting those which fit their thesis. The authors argue that Kant is the first to present us with “one single model designed to ensure peace on the national, international, and cosmopolitan levels.” (1) This is an ambitious project and only a few political philosophers have followed Kant in seeking a complete theory along these lines. Hegel is an obvious example but few 20th Century theorists come to mind.

Such a theory requires sound philosophical footing and one of the achievements of Byrd and Hruschka’s commentary is that they are particularly strong on the philosophical foundations of Kant’s system, both with regard to how the legal theory relates to the moral theory and on how the overall structure of law relates to the different concrete legal spheres. These are the elements that I will concentrate on in this review.

A perennial problem in Kant scholarship has been the question of how Kant’s legal and moral philosophies relate. Kant characterizes the universal law of right thus: “Act externally so that the free use of your choice [can] coexist with everyone’s freedom according to a universal law”. (10, Akademie Ausgabe (AA) 5:231) The problem is that while the categorical imperative (“Act only in accordance with that maxim through which you can at the same time will that it become a universal law.” (AA 4:421)) applies to purely rational beings (who are not affected by their bodily conditions) the universal law of right has to take our embodiment into account because it deals precisely with the external relations between people. The question thus becomes: how is the moral law which applies to humans qua purely rational beings related to humans qua rational embodied beings? It may be that, as some commentators have urged, our embodiment cannot play any role in the specification of actual human laws. (This is Arthur Ripstein’s position, whose Force and Freedom I reviewed in this space a year ago. Or it may be, as H. L. A. Hart has argued, following Hume, that the specific embodiment does play an important role in the sorts of laws we legislate for ourselves. This is the gist of Hart’s giant crab example in “Positivism and the Separation of Law and Morality” (Harvard Law Review, 1958, 623).

Kant himself leaves the question open, saying merely that external freedom is a postulate which admits of no further proof. This is consistent with Kant’s claim that the categorical imperative is a ‘fact of reason’, a type of postulate as well. However, this still does not solve the problem of how these two laws are related and on what authority we should believe that the external law is legitimated by reason which Kant has previously defined solely on rational and disembodied grounds.

By way of addressing this issue, I would like to address the equally vexing problem of how Kant conceives of the transition from the state of nature to the juridical state or the Rechtsstaat. As a rationalist and natural law theorist, Kant believes that natural law already exists in the state of nature. The state of nature exists in two forms, an original state of nature in which there are not yet laws, and an adventitious or contingent state of nature, in which people do, in fact (though not by necessity) stand in legal relations to each other. (Byrd and Hruschka make the convincing case that Kant took this distinction from Gottfried Achenwall, from whose text Kant lectured for many years.) The problem with the adventitious state of nature is that it only provisionally secures our rights while it is incumbent upon us to establish our rights as necessary, through rational authority. This is done by moving to the Rechtsstaat. Only the Rechtsstaat will bring about universal and lasting peace.

Kant characterizes the duty to move from the state of nature to the Rechsstaat as a postulate of public law. “In a situation of unavoidable contact, you should leave this state [of nature] with all others and move to a judicial state, i. e. the state of distributive justice.” (28, AA 6:307) This postulate, for Kant as well as for Byrd and Hruschka, remains an unfounded though necessary assumption. I would like to suggest, however, that there is an argument in Kant which can allow us to give some further support to the necessity of the move to the judicial state and hence give additional support to the laws that spring from it.

Kant, as is well known, concentrates his moral philosophy on the idea of the good will, that is, on the good intention. However, it is also a necessary consequence of willing that willing be realized in the world. Willing is not willing, Kant says, if it does not produce an action. The actions our willing results in, if they are moral, are attempts at realizing moral ends. From this we can conclude, I think without too much difficulty, that it is a natural consequence of any moral action that it produce potentially moral results in the world. In the realm of right, willing justly can then be seen as both willing properly lawful relations between people and also willing to actualize those institutions which would make these lawful relations necessary rather than contingent. Hence just willing is a matter also of willing the existence (and the means to the existence) of the judicial state. I take it then that it is no great mystery why we are obligated to move to the judicial state; it is the same reason we are obligated to realize a moral society: we can’t help doing so if we will morally, which we are anyway obligated to do.

The judicial state is organized around three types of leges or laws which, again, Kant takes from Achenwall.[1] The first two, never translated into German by Kant, and so not translated either by the commentators, are lex iuridica and lex iusti. The lex iusti is the law of external right, that is, the law for which external legislation is possible. These are law which are independent of the idea of duty itself, hence of morality. This is an important point so it is worth stressing that there are laws which, though a priori deducible from the universal law of right, are not directly derivable from the categorical imperative. They are, so to speak, mediated by our embodiment which is to say that, given the fact of our embodiment (not considered by the categorical imperative) they are a priori derivable, but not without it. Thus it is only true a priori that, given the fact that we have bodies, we may not harm each others bodies. These are natural laws applied to people who have bodies. But this category also includes laws which are not at all evident in the absent of concrete legislation. Traffic laws are laws of this sort. They are positive laws. The lex iusti is both possible in the state of adventitious state of nature and in the judicial state. The emphasis here is on the formal conditions of the law. Laws are possible for both the adventitious state of nature and the judicial state.

The lex iuridica, by contrast, is “what as substance (Materie) is also externally capable of law.” (55, AA 6:306) The lex iuridica is what, by the necessity of lawfulness established by the lex iuridica is actually legally binding. Thus, as Kant puts it, the lex iuridica is the material circumstances of our lives which are capable of being given a legal form. Thus, a particular set of actions, sighing a contract, are capable of being given legal form while another set of actions, reading a book, might not be. The lex iuridica thus provides the material for both natural and positive law. Admittedly it is at times difficult to see where we should draw the line between positive legislation of material circumstances. (Why not legislate how to read a book?) But the limit is presumably given by the basic characteristics of embodiment like vulnerability, freedom and other basic attributes.

Indeed, it is the question of the range of what is to be legislate over that is taken up in the third type of law, the lex iustitiae, which Kant defines as “the order created through distributive justice” (58), or what the authors gloss as “the order created by a judge applying the rules of laws contained in the lex iusti to those facts that have legal relevance in the concretely existing world of the lex iuridica and arriving at a final binding decision on the rights of the individuals involved.” (58) Thus the lex iustitiae is where natural law is interpreted and instantiated in terms of more fine grained positive law. While the car was invented in the late 19th Century, it did not become necessary to legislate traffic laws until the 1920s. Complementing the distinction between form and content we saw above, Byrd and Hruschka, basing themselves on Kant’s usual three part division of the categories, plausibly classify this type of law as modality which adds nothing to out cognition of what law is, but is essential for our lives under law.

[1] The oddness of the great Kant’s debt to a seemingly so obscure writer as Achenwall is already echoed by Kant’s contemporary, Thomas de Quincey, wo writes “[Kant] speaks of Achenwall, and some nameless writers, whom he calls, contemptuously, ‘worthy men’. But he ought to have know that Locke, Berbeyrac, Noodt, Burlamaqui, and all the writers on this subject of any celebrity since the era of Locke, take the same course as his own ‘worthies’, but generally with much more decision and plainspeaking.” “Kant in his Miscellaneous Essays”, The Collected Writings of Thomas de Quincey. ed. Davis Masson. vol. 8. London: 1897. 116.


Stefan Bird-Pollan is an assistant professor of philosophy at the University of Kentucky.

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