Thomas Aquinas: Core Metaphysical and Theological Concepts

Events

Events that update being. That would be the ability or potency. Thomas Aquinas distinguishes between what things are (essence) and the fact that they exist (existence). The essence is potency ('can exist or not'); existence is act.

Absolute Good

One of God's attributes. As He is absolute being, He is absolute good.

Efficient Cause

In general, it is the causal principle that in some way influences being. The efficient cause or agent is the principle of change, that which makes it possible to actualize a being. Aquinas distinguishes between the primary cause (God, the ultimate cause, not caused by another) and secondary causes (those that were caused by another).

God

Pure Act. Being in which there is no composition of matter and form, or of essence and existence. He is, therefore, the only necessary being, because His essence is His existence. He is the ultimate explanatory principle for the rest of beings.

Essence

What a thing is; the essence defines it. It is what is captured in the concept. In all beings, except God, the essence is potency relative to being, and therefore, it is distinguished from existence, the act of being. There is nothing in the essence of these beings that demands their existence, which is why they are contingent: they must have received their being from a first cause. However, in God, essence is existence, and therefore, He is necessary.

Existence

The act of being. One must distinguish between what things are (essence) and the fact that they exist (existence). Thomas Aquinas interprets this distinction through the Aristotelian concepts of potency and act: the essence is potency (it can exist or not), and existence is the act, the actualization of the essence's capacity to be.

Genus

A class that includes others of lesser extension called species. The species of the same genus can be distinguished by their specific difference. Therefore, in the definition of each species, two elements are distinguished: their genus and their specific difference. According to Aquinas, law is a species of command because law is a precept (genus) that presents specific traits, such as being enacted by reason.

Intelligence (Intellect)

In its speculative dimension, the intellect can acquire three intellectual virtues: understanding (intellectus), science (scientia), and wisdom (sapientia). Understanding is the virtue by which one comes to grasp immediately evident first principles.

Movement

The act of a being in potency, insofar as it is in potency. That is, the passage from potency to act. This passage always requires the action of something already in act, the causal agent.

Nature

What essentially defines a being, explaining its identity, activities, movements, and changes that occur naturally within it. What is natural is what conforms to the nature of a being.