Actus purus
| Category | Philosophy |
|---|---|
| Depth | Major |
| Article type | local Catholic reference article |
Definition
Actus purus means pure act: actuality without unrealised passive potency. Aquinas uses this description of God to deny that God must acquire existence, wisdom or goodness from another. God does not become divine by development. This is a claim about freedom from dependence and incompleteness, not about ceaseless physical movement.
Catholic usage
Created things are actual and potential in different respects. A real student can gain knowledge; a living tree can grow. Their actuality is genuine, but it does not exclude the possibility of becoming otherwise. Pure act names a radically different mode of reality, not simply a creature with unusually many abilities.
The distinction between passive potency and active power is essential. Lacking passive potency means not needing to be perfected or changed by another. It does not mean lacking power to act. Aquinas can therefore speak of God as both pure act and omnipotent.
Doctrinal context
The reasoning begins with the first source of actualisation. Whatever must itself receive a relevant perfection is not, in that respect, the ultimate explanation of the actuality it communicates. Aquinas's wider account of the first cause excludes composition that would require a cause of its union or actualisation. Pure act summarises the resulting denial of passive dependence.
This also explains why divine immutability is not mere stubbornness. A person may refuse to improve despite defects; pure act means there is no defect awaiting improvement. Knowledge and love are not absent, but are not acquired through the kinds of transitions by which creatures learn and mature.
Speaking this way does not turn every theological question into an easy deduction. God's free willing of creatures, temporal effects and relation to prayer require careful further explanation. The term supplies a principle for that discussion; it is not a licence to dismiss the reader's difficulty.
Distinctions and safeguards
Pure act is not identical with performing every possible action. God's freedom is not a passive incompleteness waiting to be repaired. Nor does perfection mean being able to make contradictions true. A contradiction fails to identify a coherent possible object of power.
If God creates a changing world, must God change?
Aquinas distinguishes a change in the creature from an alteration in the divine act of knowing and willing. An effect can begin at a particular time without God acquiring a new intention through discovery or pressure. This answer presupposes a non-temporal mode of divine life; it cannot simply be pictured as a very long human life. The remaining task is to explain that distinction coherently, rather than imagine God waiting and then deciding.