Here lies an apparent contradiction how is there unity in the diversity of the universe. Even the word bespeaks of the contradiction, uni and diverse share roots with universe. Parmenides denied one half of the apparent paradox, manyness. This eliminates change as well because change is just a manyness in time, before and after. He was a monist/pantheist everything is one god, the universe, everything because there is only one thing. The direct opposite can be found in Heraclitus he denied any permanence, saying that all reality was like a river that you could never step into twice. Plato resolved the problem by distinguishing two worlds, matter where there is manyness and the world of the forms where there was unity. Aristotle joined Plato’s two worlds with substance being matter and form together.
Aquinas commented on the error of Parmenides and other monists with this:
“They fell into error because they dealt with being as though it were a univocal concept and an essence . . . this, however, cannot be done, for being is analogous . . . Parmenides argues as follows: outside of being there is nothing but nonbeing, and that which is not being is nothing. Since being is one, whatever is outside the one is nothing.’ From this argument of his it is clear that Parmenides was thinking of the concept of being, which appears always to be one and the same, and univocal, for it is unthinkable that something be added to the concept of being so that one concept of being be distinguished from another. For that which would be added to being must necessarily be something outside of and distinct from being. But the only thing outside of or extraneous to being is nonbeing or nothing. Hence it appears that the notion of being cannot be modified, cannot be anything but one, unique, and univocal.”If there is only one thing, individuality is an illusion. However, radical pluralism is nominalism: it denies universal ideas existence, and reduces them to mere words. But, the evidence of our senses shows us both oneness and manyness. Any good philosophy has to account for all possibilities, not ignore what we don't like or want to understand.
As Professor Kreeft says, "Aquinas explains the oneness of beings by the fact that they all share the act of existence, which is itself one and the same simple act. But beings are different because this act of existence is received into many different essences."
I also like this quote, "Aquinas calls God the pure act of existence unlimited by any finite essence."
This is not to reduce God to a philosophical abstraction, just a way of talking about God that makes sense. This does not change how God is the God of Abraham, Isaac etc. This isn't about just philosophy, it's about the real world as well.
Everything that is real shares a kinship in the act of existence. And, as God is the infinite pure act of existence this is one way in which God is omnipresent. "God is existence itself, and existence itself is most intimately present at the heart of every being. Therefore God is most intimately present at the heart of every being."
So here we have it, God is everywhere but this is NOT pantheism, because it’s the act of existence and that transcendent fact that so is intimately present to everything.
Prof Kreeft goes into a long discussion about Angels and their differences from humans, but I'm not going to go into it here.
This is important to Aquinas' philosophy: "Like Aristotle, Aquinas defines change as the transition from potentiality to actuality, and he distinguishes two different kinds of change: accidental change and substantial or essential change. When I get older, smarter, or fatter, that’s only change in accidents, but when I die, that’s a change in essence."
Something remains the same in accidental changes, I am still me even though my entire body's cells have died and been replaced by new cells.
Each person also goes through essential change twice, when we are conceived and when we die. Corpses are not people nor any kind of a person.
Again "following Aristotle," seems Aquinas was quite enamored with Aristotle's philosophy, "Aquinas distinguishes four causes, four kinds of causality: form and matter are the two intrinsic causes, the formal cause and the material cause; and the efficient and final causes are the two extrinsic causes."
This final point, which Aristotle and Aquinas call a "final cause," has fallen out of modern usage, possibly because it's not considered scientific. All things act in definite ways. Puppies always become dogs (assuming they don't die prematurely), Birds fly, fish swim etc. Puppies never become horses and rocks can't swim and never will. This is final causality, things are directed to their specific ends.
As Aquinas argues in one of the five ways, everything that begins to exist needs an efficient cause to account for its existence. If a thing itself were its own sufficient reason, it would have to exist always. Either this sufficient reason is eternal or it would have to give existence to itself—which is impossible: nothing can give what it doesn't posses.
Again, sorry no picture!