On the Power of God

The central distinction is between God's absolute power (potentia absoluta) and his ordained power (potentia ordinata). Absolute power refers to what God can do considered in himself, apart from any decree: he can do anything that does not imply a contradiction. Ordained power refers to what God has freely decreed to do in the order of creation and redemption . The distinction matters because it allows Aquinas to affirm both divine omnipotence and the stability of the created order. God could have created a different world, but he has freely chosen this one, and his ordained power is the order he has established. The distinction became crucial in later medieval debates about God's freedom and the contingency of the world.

For Aquinas, the principle of non-contradiction is not a limitation on God's power but a condition of intelligibility. To say that God cannot make a square circle is not to say that God is weak; it is to say that 'square circle' is not a possible thing to be made. The phrase 'God can do all things' is to be understood as 'God can do all things that are possible,' and the possible is defined by the absence of contradiction . This position rejects the voluntarist view, associated with some later medieval thinkers, that God could have made contradictions true if he had willed to. For Aquinas, God's power is identical with his essence, and his essence is intelligible; the laws of logic are not external constraints on God but expressions of his own rationality.

On the Power of God is a disputed question, conducted around 1265–1266, roughly contemporaneous with the beginning of the Summa Theologica (begun around 1265). It treats many of the same topics that the Summa would later systematize, including God's power, creation, preservation, miracles, grace, and predestination . The disputed question format allows for more extended and exploratory treatment than the Summa's articles, and scholars often compare the two to track the development of Aquinas's thought. The work is not a draft of the Summa but a distinct exercise in the same genre as the Disputed Questions on Truth. Readers who know the Summa will find here a more sprawling and argumentative Aquinas, working through problems at greater length.

The English translation by the English Dominican Fathers, published by Burns Oates and Washbourne between 1932 and 1934, is the standard complete English version of On the Power of God . It is a serviceable translation, generally accurate and readable, but it reflects the Thomistic idiom of its time: it tends toward literal rendering of Latin technical terms and does not include the extensive notes and apparatus that contemporary scholars expect. There is no modern critical English translation with updated apparatus, though the Latin text is available in the Leonine edition and in the Marietti edition. Readers who want to engage the text seriously should consult the Latin alongside the translation, and should be aware that the translation's terminology may not match contemporary usage.

The most common misunderstanding is that absolute power means God can do anything at all, including contradictions, and that this makes the created order arbitrary. Aquinas explicitly denies that God can do the logically impossible, and he insists that God's ordained power is a free but rational decree . A related misunderstanding is that the distinction between absolute and ordained power was a late medieval innovation, associated with nominalism. In fact, the distinction is present in Aquinas and in earlier scholastic thought, though it was developed in different directions by later thinkers such as Duns Scotus and William of Ockham . The work is a contribution to classical theism, not a precursor of voluntarism. God's power is the power of a rational agent, not of an arbitrary will.