Intellect: faculty in the soul ordered to know the truth
Will: faculty in the soul ordered to do the good
Concupiscible appetite: pleasure emotions regarding good (love, desire, joy) and evil (hatred, aversion, sorrow)
Irascible appetite: pain emotions regarding good (hope, despair) and evil (courage, fear, anger)
Example: what are the four causes of a wooden chair?
Material cause: that out of which something is made. Example: wood
Efficient cause: that by which something is made. Example: the carpenter
Formal cause: that into which something is made. Example: the shape of the chair. (Note: the formal cause is not always the shape)
Final cause: that for the sake of which something is made. Example: sitting.
Matter: that stuff or matter out of which a thing takes its existence.
Form: the manner in which the stuff is arranged in order to make it exist.
Example: the matter of an apple is its sugar, carbon compounds and other stuff which makes up the apple. Its form is its “appleness,” or the way in which its matter is arranged to make it an apple. In other words, if all the matter of the apple were separated and piled into a heap, you would have the matter of an apple but not its form.
Example: a material heretic holds to the matter of heresy, which is an error against the faith. He may also be called an “erring theologian.” In other words, he has not been formally corrected. A formal heretic holds this error obstinately, so the manner in which he holds this error is the manner of a heretic. In other words, he has been formally corrected and obstinately persists in his error. Before the bull of excommunication, Fr. Martin Luther was only a material heretic. After he publicly burned the bull, he became a formal heretic.
Substance: that without which a thing cannot be what it is.
Accident: that without which a thing will remain what it is.
Example: an apple has its own “appleness,” which constitutes its matter according to the form of an apple – this forms its substance as an apple. However, between apples, there are differences of size, shape, or color which nevertheless do not change apples into something different. Thus these properties may be called accidents, since they are not a part of an apple’s substance. In other words, take away an apples color or change it, and you still have an apple. But take away an apple’s substance, and you no longer have an apple.
Example: after the consecration, the substance of the bread and wine become the substance of the Body and Blood of our Lord (transubstantiation). Therefore, since the substance of bread and wine is gone (while their accident remain), the Blessed Sacrament may properly receive worship (latria) from the faithful in the same manner as we worship God Himself.
These terms are similar to their grammatical equivalents. The subject is one who acts upon an object. The boy (subject) kicks the ball (object). However, when we speak “objectively” about a man, we take him as our object and look at him from the outside.
Example: the Council of Florence states that no one who is not subjected to the Roman Pontiff can be saved. Or elsewhere it is said that baptism is necessary for salvation. These are both salvation considered from the objective aspect, with a man as the object.
On the other hand, St. Thomas teaches that a man can be saved without baptism, citing Augustine in reference to a martyred catechumen’s desire to be baptized (III q68 a2). Thus objectively, this man cannot be saved since he was not baptized. However, considered subjectively (from the man within himself), he can be saved by virtue of his desire to be baptized. Put another way, not all those who are objectively submitted to the Roman Pontiff will be saved, because subjectively they are apostates.
Potency: having the potential or power to do a thing. Example: a fertile man has the potency to become a father.
Actuality: when potency is put into action to make a potential reality an actual reality. Example: when a man begets a child, he is no longer a father in potency, but in actuality.