Entry 0084: The Metaphysical Principles of
‘Essence’ and ‘Act of Being’
‘Essence’ and ‘Act of Being’
The expression ‘actus essendi’ is a technical term used by Aquinas. It has a restricted, specialized meaning. ‘Actus essendi’ is the metaphysical principle that goes ‘side by side’ with the metaphysical principle ‘essence’ in a subsisting extramental thing.
Three points of reference are indicated here. One, the real finite thing itself existing in the external world; another, the ‘essence’ which makes the thing to be what it is; and yet another, the ‘actus essendi’ which places both the thing with its ‘essence’ in actual existence.
In the real world ‘essence’ and ‘actus essendi’ are inseparable metaphysical principles. The metaphysical principle of ‘actus essendi’ always appears instantiated in an ‘essence.’ And the ‘essence’ of the thing is what put limits to the thing’s participation in ‘actus essendi.’
For Aquinas, the ‘act of being’ is the most profound perfection of a thing; it is an internal incommunicable metaphysical principle inseparable from the thing itself, from the ‘essence’ of the thing, and from anything that exists in the thing.