Kant’s views on peace, cosmopolitanism and the unity of international law have been often considered as an inspiration for liberal internationalists looking for an authoritative philosophical source. Notwithstanding this appreciative attitude, Kant’s thought should be regarded as something more than just a dusty old glory blessing for open-minded and progressive politicians and lawyers. The rationale that accompanies Kant’s idea of a ‘cosmopolitan constitution’ (Weltbürgerliche Verfassung), which sometimes he refers to also in terms of a ‘cosmopolitan commonwealth’ (Weltbürgerliches gemeines Wesen) or as ‘a cosmopolitan whole’ (Weltbürgerliches Ganze), is fully intelligible only if considered as a conceptual framework for the determination of the idea of unity and legitimacy of international law. To understand Kant’s reasoning let’s imagine to having to explain the legitimate conditions under which domestic and international law have a title to oblige individual and states to comply with international legal standards. For Kant, reader of Hobbes, this initial condition is the state of nature. The state of nature is a condition deprived of law and justice. Here, the question of justice and coercion arises only once individuals interact with the environment by grabbing into their hand the surrounding objects and lands and claiming private property upon. Kant solves these sorts of difficulties by resorting to the idea of a public authority to which, collectively, individuals in the state of nature appeal to. This might well be the sovereign state as a political entity but, were this Kant’s solution, then no substantial difference would appear with Hobbes’s views.
Kant, instead, sees the exiting from the state of nature as something characterized by a persistent contradiction between: a) individuals’ entrance into the civil condition of the states, and b) the condition of anomy between states in the international order.
It seems, indeed, that the difficulty here consists in the fact that, differently from Hobbes, states alone here cannot exhaust the requirements for overcoming a natural condition deprived of justice by entering into a civil condition. Indeed, no justice would be achieved among them if it were sufficient to appeal to an only internal condition of justice within states and not also to establish a civil condition among them. But since for Kant we cannot superimpose an international order against the will of the states, then, the problem remains on how to find a way to overcome a condition of absence of international justice.
This way to frame the Kant’s discourse on the relation between the domestic and the international level is a way to understand the opposition that he famously draws between the necessity to create a world state republic as something which is right in thesi (in theory) according to a theory of public international law, and what instead can be realistically admitted in hypothesi (in practice), from the point of view of the states.There appears here a confrontation between two points of view: an all-encompassing idea of a positive world state republic shaping the legitimacy of the international order and the idea of the limited state point of view protecting autonomy of state sovereignty. The ‘correction’ Kant introduces to Hobbes’s idea of a fulfilment of a natural condition by a simply entering into a civil state framework considers that if one imagines individual entrance into a juridical condition, no matter what is the entity in which one lands, no lawless condition of a state of nature can be readmitted back on the pain of contradiction, that is, on the pain of contradicting the sufficiency of the initial argument for exiting the state of nature.
How to solve the riddle? Given that neither a Hobbesian international state of nature, nor a positive world state republic would be a solution, how to construct an international civil condition without infringing upon states’ sovereignties? By distinguishing between what is right in theory and what instead holds in practice, Kant thinks that we can start from what is ‘a league of states’, a negative surrogate of the world state republic which maintains a purely self-defensive purpose. But this is though only an imperfect solution. It avoids the double contradiction mentioned above while remaining an insufficient tool for establishing a long-lasting international peace among state entities. Therefore, the league of states is only a pro tempore solution, something to start with, but not an end-point solution for the establishment of legitimate and stable relations among states.
This bears two implications: first, the league of states, what Kant sees as possible in hypothesi, from the point of view of the states, must be improved in its delivering of justice and establishment of a rule of law; second, a world state republic cannot be taken as a positive instantiation but only as a regulative idea re-joining the plurality of states within one single ideal scheme of law.
It is at the conjunction of these two conceptual currents that Kant introduces the idea of a cosmopolitan constitution as a solution for the overcoming of a condition of lack of justice among states in the international realm and as the only way to respect states’ sovereign wills when deciding upon how to further the conditions of a voluntary league of states. Just relations among states must be respondent to the principles of a global constitution which defines basic rights for citizens both in their respective domestic constituencies as well as in their relation as foreign visitors to other states. This explains why for Kant the core of cosmopolitanism consists in “the right to visit”, namely, in the right to be hosted temporarily in another state. There are a multiple reasons for Kant according to which one can request to be a foreign visitor: they range from asking asylum to submitting commercial trade proposals. There is no other way, for Kant, to seek peace than by installing an international framework under public constitutional laws and, I believe, he was right about that.
The author is an Associate Professor of Political Philosophy at the University of Rome II.
 Immanuel Kant, Towards Perpetual Peace, in M. Gregor (ed.), Immanuel Kant: Practical Philosophy (Cambridge University Press, Cambridge, 1996 ), 329.
 Immanuel Kant, On the Common Saying: That May be Correct in Theory, in M. Gregor (ed.), Immanuel Kant: Practical Philosophy (Cambridge University Press, Cambridge, 1996 ), 308.
 Immanuel Kant, Critique of the Power of Judgment, P. Guyer (ed.), (Cambridge University Press, 2000 ) 300.
 Supra note 1 at 347.
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