Definitions

An act of being/existence = that on account of which something exists, that which is signified by the predicate ‘exists’ in this thing

A being (entity) = that which exists, that which has an act of being

A potential being = that which can, but does not, exist; something that is in potentiality

An actual being = that which does exist [Note: a being and an actual being are the same; therefore, ‘potential being’ is not a species of ‘being’, in the same way as ‘fake diamond’ is not a species of ‘diamond’]

A form = that which is signified by a common term ‘F’ in a thing, referred to as the F-ness of this thing, so that the thing is actually F if and only if its F-ness actually exists

A privation = the lack of a form in a definite kind of subject that could and ought to have the form by nature, but does not have it (e.g., blindness is the privation of sight in animals, if they lack sight; but even if stones do not have sight either, they are not blind, because they could not have sight anyway)

Matter or subject (broadly speaking) = that which can have both a privation and the corresponding form successively (i.e., which is in potentiality towards both the form and its privation through change)

Substantial form = a form, the act of being of which is the same as the act of being of the thing whose form it is; so that for the thing to be is for it to have this form in actuality; whence the thing cannot stay in existence if it loses this form

Accidental form = a form, the act of being of which is not the same as the act of being of the thing whose form it is; so that for the thing to be is not for it to have this form in actuality; whence the thing can stay in existence even if it loses this form

Subject (strictly speaking) = the subject (broadly speaking, see definition above) of accidental forms

Matter (strictly speaking) = the subject (broadly speaking, see definition above) of substantial forms

Principle (epistemologically) = an indemonstrable proposition, known a priori (on the basis of understanding it alone, i.e., on the basis of just having the concepts that make it up), which, therefore, can serve as a first, undemonstrated premise in demonstrations

Principle (ontologically) = a first, or primary constituent, or precondition of some phenomenon in actual reality

Principles of change: privation, form (formal cause), matter (material cause), agent (efficient cause), end (final cause)

Cause = some entity, the actual being of which accounts for the being of something else

Kinds of causes of change and/or of being: form (formal cause = that which accounts for the being of its subject by its actuality), matter (material cause = that which accounts for the being of the thing composed of matter and form by receiving the form in actuality), agent (efficient cause = that which accounts for the being of something else by its action), end (final cause = that which accounts for the action of the agent as that for the sake of which the action is performed)

Modes of causes: 1. proximate (more particular, posterior) vs. remote (more universal, prior); 2. per se vs. per accidens; 3. actual vs. potential

1. In a chain of simultaneously working causes of the same kind the proximate cause is one that immediately causes its effect, while a remote cause is one that causes the same effect by the mediation of some intermediary cause(s)

2. A per se cause (relative to a certain causal relationship between this cause and its effect) is the cause denominated on account of its causally relevant feature (i.e., on account of that feature which accounts for its bringing about and/or maintaining the effect in the causal relation in question). A per accidens cause is a cause that is not per se.

3. An actual cause is one the actual being and/or operating of which is required for the actuality of its effect, so the actual being (and/or operation) of such a cause is always simultaneous with the actuality of its effect (example: electricity is the actual cause of the light of the lamp, break the circuit, and the light is gone); a potential cause is one that only habitually accounts for the being of its effect, but the actual being and/or operation of which is not required for the actuality of the effect (example: buildings usually survive their builders, children usually survive their parents, etc.)