Essence & Existence — The Second Foundation

Aristotle's and Aquinas's distinction between essence and existence.

Essence answers to what a thing is, while existence, or being, answers to that it is, or the fact that it exists.

— The Thomistic Institute

Alongside act and potency, the Five Ways lean on a second, closely related distinction: essence and existence. Aristotle first pried the two apart; Aquinas made their relationship the sharpest point of his metaphysics.

The puzzle of contingent being. You can know exactly what something is without knowing whether it exists. You know what a unicorn or a phoenix is, yet neither one is real. So in every ordinary thing there is a real gap between what it is and the plain fact that it is here at all. That gap is the clue Aquinas follows all the way to God.

The distinction, in plain terms:

• Essence: what a thing is: the kind of thing it is, its nature or definition. The essence of a dog is to be a certain kind of living animal.
• Existence: that a thing is: the sheer act of being, the fact that the thing is actually there rather than merely possible.

In everything we meet, essence and existence are genuinely two different things. A thing's nature does not include its own existence — which is why you can fully understand it and yet it may not exist, and why it can come into being and later pass away.

Existence is received, not owned. Because a creature's nature does not contain its own existence, being is something it has, not something it is. Its existence has to be given to it by something else, and kept going for as long as the thing lasts. Here is the principle Aquinas draws from this:

Everything, then, which is such that its act of existing is other than its nature must needs have its act of existing from something else.

— St. Thomas Aquinas, De Ente et Essentia, ch. 4

The dog does not account for its own being; its existence is derived, dependent, borrowed at every moment.

Why this matters for the Five Ways. Several ways, especially the Third Way from contingency, are really arguments about essence and existence:

1. In every ordinary thing, essence and existence are distinct — such a thing could not exist.
2. Whatever does not exist through its own essence has existence given to it by another.
3. This cannot regress infinitely through things that are themselves composed of essence and existence, for the whole chain would then have no source of being.
4. Therefore there must be something whose essence just is existence — Being Itself, existence with no potential for non-existence — the source of all being.

This being, whose very nature is to exist, Aquinas says, is what everyone understands to be God.

Keep this distinction in mind as you read the ways below: wherever you see contingency, dependence, or a thing that might not have been, you are watching existence being received from another.