This paper sought to show the way in which Kant, in his theory of law and politics, argues for the existence of the legal duty to leave the state of nature and enter the civil state. As opposed to ethical duties, the fulfilment of legal duties can be forced upon a person by other people. Coercion is important in the context of this paper because, according to Kant, right is always connected with an authorization to use coercion. The right of intelligible possession as an acquired right already existing in the state of nature is the basis of the legal duty to leave the state of nature and enter the civil state. The right of intelligible possession, which refers to the possession of external objects, or possession independent of the empirical conditions of space and time, implies the duty of all others to refrain from using the objects we first possess, but also the moral authorization of coercion over those who refuse to do so. However, since in the state of nature there is no public authority that articulates and enforces the law through general laws, coercion is arbitrary and depends on particular interpretations of legal situations. The arbitrariness of coercion implies the possibility that the freedom of the individual, which is externally manifested through the right of intelligible possession, will be endangered. For this reason, others can be forced to enter the civil state with me, submitting to the public authority under the same conditions. The public authority makes rights of possession explicit and secures them, and is thus a necessary condition for the fullness of human freedom.