All law comes from the eternal law of Divine Reason that governs the universe, which is understood and participated in by rational beings (such as men and angels) as the natural law. The natural law, when codified and promulgated, is ('human law'). In addition to the human law, dictated by reason, man also has the divine law, which, according to Question 91, is dictated through revelation, that man may be "directed how to perform his proper acts in view of his last end", "that man may know without any doubt what he ought to do and what he ought to avoid", because "human law could not sufficiently curb and direct interior acts", and since "human law cannot punish or forbid all evil deeds: since while aiming at doing away with all evils, it would do away with many good things, and would hinder the advance of the common good, which is necessary for human intercourse." Human law is not all-powerful; it cannot govern a man's conscience, nor prohibit all vices, nor can it force all men to act according to its letter, rather than its spirit. Furthermore, it is possible that an edict can be issued without any basis in law as defined in Question 90; in this case, men are under no compulsion to act, save as it helps the common good. This separation between law and acts of force also allows men to depose tyrants, or those who flout the natural law; while removing an agent of the law is contrary to the common good and the eternal law of God, which orders the powers that be, removing a tyrant is lawful as he has ceded his claim to being a lawful authority by acting contrary to law. The way which leads to God is Christ, the theme of Part III. It can be asserted that the incarnation was absolutely necessary. The "Unio" between the Logos and the human nature is a "relation" between the divine and the human nature, which comes about by both natures being brought together in the one person of the Logos. An incarnation can be spoken of only in the sense that the human nature began to be in the eternal hypostasis of the divine nature. So Christ is "unum" since his human nature lacks the hypostasis. The person of the Logos, accordingly, has assumed the impersonal human nature, and in such way that the assumption of the soul became the means for the assumption of the body. This union with the human soul is the "gratia unionis", which leads to the impartation of the "gratia habitualis" from the Logos to the human nature.