Metaphysics, part three

There are two kinds of changes: accidental and substantial. In an accidental change, there is change in a being, and that being remains what it was from the beginning through the end of the change. A kitty growing into an adult cat, or the colour or amount of my hair changing: I'm different, but I'm still me. A substantial change is a change where the being at the end of the change is no longer the same being, but a different one; here, the essence of the being changes. Just to be provocative, an example of this kind of change is Transubstantiation. The principle of self-identity in a being is its substance, what it is; the principle of change in a being is its accidents. Substance is the being, and accidents are the things predicated of a being.

For angels, since they are pure spirit, the principle of individuation is form, rather than matter. So each angel is its own species: they aren't related to one another, as we are. Each angel is radically distinct from all the other angels. Since only matter individuates human persons, our bodies are, again, a very important part of us, and help form our identities.

The principle of causality states that every being that lacks the sufficient reason for its own existence in itself, must have an efficient cause (ie something which by its action is responsible for the existence of the first being). Other formulations of this statement include:
*Every being that begins to exist needs an efficient cause (because a being that does not exist cannot cause itself to exist). This is used as an argument for God, and is what brought me out of atheism into deism: The universe began at the Big Bang. So there wasn't the universe before the Big Bang. So God must exist, as the cause of the Big Bang/the state of existence of the universe.
*Every being composed of essence-existence or matter-form requires an efficient cause, because there has to be some outside efficient cause that unifies them in composing the being: The co-principles can't exist on their own, so they can't cause each other; the components don't include each other; so something has to bring them both into being.
*Every finite being requires an efficient cause; finite beings participate finitely in existence, and their participation refers back to the being that possesses existence infinitely.

From these formulations (and some I left out) a self-sufficient being has six characteristics: it will be uncaused, eternal, unchanging, simple, not a part of any system, and qualitatively infinite in perfection.

Cause and effect are a single event; they can't be separated from one another in time, or their actual connection to each other is broken.

St Thomas teaches that God's existence can be demonstrated, from those effects of his which are known to us.