Michael Austin writes that an implication of this modified divine command theory is that God cannot command cruelty for its own sake; this could be argued to be inconsistent with God's omnipotence. Thomas Aquinas argued that God's omnipotence should be understood as the ability to do all things that are possible: he attempted to refute the idea that God's inability to perform illogical actions challenges his omnipotence. Austin contends that commanding cruelty for its own sake is not illogical, so is not covered by Aquinas' defence, although Aquinas had argued that sin is the falling short of a perfect action and thus not compatible with omnipotence.