Man's moral responsibility for his actions is a tenet of Islamic revelation which no Muslim has ever tried to reject. Likewise, the notion of God's omnipotence, which the Qur'ān teaches, has never been challenged by Muslims. However, there is a great difficulty in explaining how true moral responsibility coincides with God's omnipotence; if God creates all things, He also creates man's actions, and this being the case, man cannot be responsible for them. As is well known, the Mu'tazilite solution to the antinomy of God's omnipotence and man's responsibility consists in affirming man's capability, granted to him by God, of creating his own works. Adhering to their principle of God's justice, the Mu'tazilites asserted that if God were to create a man's unbelief while commanding him to believe, He would be unjust in punishing him for unbelief, since the man could not, in this situation, help but disbelieve. According to them, ought implies can. In upholding man's responsibility for his own actions, the Mu'tazilites saved God's justice, but according to the Ash'arites, detracted from God's omnipotence. The Ash'arites taught that since God is the sole creator, He creates human actions. In order to safeguard both God's omnipotence and man's responsibility, al-Ash'arī, having been influenced by the teaching of al-Najjār, developed a theory of kasb (lit. acquisition) according to which God creates man's actions while man appropriates them and thus becomes responsible for them.