In the first way of Aquinas it is proved that there exists an unmoved mover (or unchanged changer or even better, actualizer which was not actualized). It is often claimed that God is pure act without any potency; but I seem to think that in the first way it is proved that first mover is not moved; but it was not proved that first mover is unmovable.
Why does the first mover need to be unmovable? Why can it not have some potencies which are not ever actualized?
The philosophical axiom that
something cannot give what it does not have
nemo dat quod non habet
(cf. I q. 2 a. 3)
applies here.
If the First Mover were movable (i.e., not pure actuality, actus purus), it would lack something (for example:* the ability to move other things), and it could not give what it lacks to others (in the example: it could not change others). This is a contradiction (in the example: because we do observe that things change). Thus, the First Mover must be immovable.
*Any (absolute, not relative) perfection could be given as an example of what the First Mover could lack, and the argument would remain. Other examples: immateriality, omniscience, justice, omnipresence, etc.:
If the First Mover lacked immateriality, it could not give immateriality to creatures; but, we know that there are immaterial creatures; ergo….
Or: If the First Mover lacked all knowledge, it could not give knowledge to creatures; but, we know that there are creatures with knowledge; ergo….
Or: If the First Mover lacked justice, it could not give justice to creatures; but, we know that there are creatures with the virtue of justice; ergo….
Or: If the First Mover were localized to one place, it could not make creatures localized to no place; but, we know that there are creatures not localized to one place (e.g., purely intellectual beings, the angels); ergo….
Etc.
See Aristotle Physics, Bk.VII :
[242a50] Since everything that is in motion must be moved by something, let us take the case in which a thing is in locomotion and is moved by something that is itself in motion, and that again is moved by something else that is in motion, and that by something else, and so on continually: then the series cannot go on to infinity, but there must be some first mover.
Thus, Aristotle's argument is based on the rejection of an infinite regress.
Regarding Aquinas, see Divine Simplicity :
According to the classical theism of Augustine, Anselm, Aquinas and their adherents, God is radically unlike creatures in that he is devoid of any complexity or composition, whether physical or metaphysical. Besides lacking spatial and temporal parts, God is free of matter-form composition, potency-act composition, and existence-essence composition.
See Augustine, The City of God, Bk.XI, §10 :
There is, then, a Good which alone is simple, and therefore alone immutable, and this is God.
Thus, if God is immutable, he cannot have "potentialities" that are not actualized.
Here is the question:
Why does the first mover need to be unmovable? Why can it not have some potencies which are not ever actualized?
This answer only tries to address the first question hoping the second will fall in place.
One way to view this is to see the first mover as not a kind of body that moves other bodies such as one might think of a billiard ball moving another billiard ball. If it is not a body, the idea of some body moving it is not meaningful. Hence one should expect this immaterial reality to be unmoved.
Initially this seems odd until we remember that we don't think of the billiard ball actually coming in contact with the other billiard ball. What contacts both balls are immaterial fields that move or change both balls in some way.
Although the actual existence of these immaterial fields is often taken for granted, some physicists do question them as being real. For example, on page 42, Marc Lange quotes Alfred O'Railly's 1965 textbook, Electromagnetic Theory:
The assertion [of the electromagnetic field's reality], taken by itself apart from the quantitative force-law is scientifically otiose....It is merely the physically irrelevant statement of a metaphysical conviction....This is certainly not a legitimate physical theory at all; it is the confusion of metaphysical belief with metrical physics....
The question of the existence of unmoved movers can be viewed as analogous to questions about the reality of fields.
To carry this further consider what it means for there to be a "first" such unmoved mover. Dominic O'Meara describes Plotinus going beyond Plato's Forms to assert the reality of the simpler One as similar to what a scientist does when looking for a simpler, more unifying, explanation: (page 46)
Throughout the history of philosophy and science can be found the idea that everything made up of parts, every composite thing, depends and derives in some way from what is not composite, what is simple. This idea might be called the 'Principle of Prior Simplicity'. The Principle of Prior Simplicity has not lost its appeal: it still inspires scientists in their efforts to reconstruct the generation of the elements from an earlier, simpler state of the universe, and similar explanatory patterns, deriving the complex from what is less complex, can be observed, for example, in biology.
Use of terms like actualities and potentialities may specialize the description of unmoved movers toward particular philosophies. Shifting this analogically to fields may offer different descriptions and suggest other reasons to justify belief in unmoved movers.
The existence of such reality as immaterial unmoved movers and fields is questionable but if they are not real, as Alfred O'Railly insists they are not, some other explanations for the motion of bodies would be required.
Lange, M. (2002). An Introduction to the philosophy of physics: Locality, fields, energy, and mass. Blackwell Publishing.
O'Meara, D. J. (1995). Plotinus: an introduction to the Enneads. Oxford University Press.
It has been postulated by some philosophers that God is the Universe.
Theologians have claimed that God is unmovable by any force other than itself.
Of course it can move itself, as it is dynamic and said to be omnipotent.
There are certain basic properties however which in God never changes.
That it is eternal and infinite, for example, may never change. In that respect, it is immovable.
Therefore if God is the universe, i.e. Reality itself, if anything had power to change it, everything -- reality as we experience it, perhaps even all consciousness -- would cease to exist.
There would be nothing left, only Death.
Therefore it must be immovable by anything other than the totality of itself. That is why it is called the immovable mover.
That is not to say that it cannot respond to acts of freewill, by humans for example.
Let us imagine hypothetically that humans decide to destroy their own habitation, Earth. Whether or not they succeed, the Universe will be affected by and will respond to such activity.
But although humans may be able to destroy the Earth, the Sun, the Moon, our own solar system, galaxy, and even ourselves as a species, we cannot destroy the Universe, no matter how hard some may try.
Meanwhile the universe can and does have freedom to move (or change) itself. Perhaps it expands and contracts like an enormous heartbeat, producing (or creating) "Big Bangs" and "Black Holes" and "galaxies" and other interesting phenomena.
Surely God can quite easily heal itself and recover from any and all assaults on it by certain members of the human species who, whether intentionally or foolishly, choose to destroy themselves and others.
And if not, then eventually everything would simply cease to exist and be replaced by death or nothingness.
An idea which unfortunately doesn't seem to bother some people.
However Justice (universal justice) is supposed to prevent that from happening, suggesting that if it indeed cannot happen -- if nothing can destroy the universe -- then God really is the immovable mover.
You must remember that Aquinas was first and foremost a priest. Therefore, he could not just suddenly "discover" that idea of God (especially Christian idea of God) is contradictory to logic. Instead, he was trying to come by reason to the same conclusions other came by faith.
We must now ask ourselves why God must be unmovable. Something that is moveable is by definition changeable. Notion that God could change was terrifying for theologians : this would mean that God's plan could change, truth could change (truth is what God makes true), even teachings and prophecies from the Bible could be invalidated - definitely not a good thing.
Aquinas, as a Christian priest, could not accept idea of world(s) being in perpetual (uncaused) motion, therefore he accepted Aristotle's idea of first mover. He also accepted idea that something could not give what it lacks, which is a bit shaky, as certain qualities could be transformed (for example gasoline transforms it's chemical energy into kinetic energy of a car, i.e. movement). Therefore, he had a problem how would his first mover, being unmovable God, make other things move.
He "resolved" this this problem by putting God completely out of physical time and space, making him a category of his own. Aquinas makes God act with his willpower (Pure Act) , without needing any physical attributes for that act like other beings and objects. These physical attributes are called potencies in his works, somewhat similar to potential energy in latter physics.
