Causal adequacy principle

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The causal adequacy principle (CAP) is a philosophical claim made by René Descartes that the cause of an object must contain at least as much reality as the object itself, whether formally or eminently.

Descartes defends this principle by quoting Roman philosopher Lucretius: "Ex nihilo nihil fit", meaning "Nothing comes from nothing". —Carus, Lucretius (1947). De Rerum Natura. Oxford University Press. pp. 146–482. 

In his meditations, Descartes uses the CAP, to support his trademark argument for the existence of God. Descartes' assertions were disputed by Thomas Hobbes in his "Third Set of Objections" published in 1641.. Amongst other contemporary objections, CAP comes under difficulties when it comes to the idea of creation and beginning. If one accepts CAP one has to necessarily accept that there is no beginning (thus no end) in anything. Such an objection, although controversial, is justified because if God is supposed to be the creator of all, CAP would indicate that he is caused by something as big or greater. Such a claim is not logically possible if one accepts that God is in fact perfection incarnate. The same goes for there having been a Big Bang. CAP would again indicate that a Bigger Big Bang must have caused the one we know as the beginner of our universe. This causes what is known in Philosophical circles as Infinite Regress.

René Descartes was not the founder of this philosophical claim. It is used in the classical metaphysics of Plato and Aristotle, and features eminently in the works of Thomas Aquinas.

Jargon explained

• A "cause" is that which brings something into effect.
• If an item has the quality X formally, it has it in the literal or strict sense.
• If an item has the quality X eminently, it has it in a higher or grander form.

CAP in practice

To demonstrate this, a person can possess money formally by holding it on their person, or by storing it in a bank account. Similarly, a person can eminently possess money by owning assets that could readily be exchanged for it.

Descartes offers two explanations of his own:

• Heat cannot be produced in an object which was not previously hot, except by something of at least the same order of perfection as heat.
• A stone, for example, which previously did not exist, cannot begin to exist unless it is produced by something which contains, either formally or eminently everything to be found in the stone.

Descartes goes on to claim that the CAP not only applies to stones, but also the realm of ideas, and the features that are seen as part of the objective reality of an idea.