Few of us have a beef with the first premise of the argument from motion:
1. Evident to the senses is motion. (Premise)
Things change, and we know this through observational experiences.
2. Everything in motion is moved by another. (Premise)
No potentiality can actualize itself. An acorn doesn't become an oak tree inexplicably. It requires external causes to actualize its potentiality: soil, water, sunlight, etc. (I repeat these analogies for the sake of possible newcomers to the blog.)
Now, I have defended formulated the third premise in the past like this:
3. If there is no First Mover, there will be no motion. (Premise)
I have defended this by pointing to various other illustrations that show once the cause of the set's motion is removed, then the motion of the set itself will cease. A watch without a spring will have no gears in motion. A train without an engine will have no boxcars in motion. Likewise, if the universe as a whole has no First Mover, then none of its parts will be in motion, which is obviously false.
From (1) through (3) it follows that:
4. Therefore, a First Mover exists. (From 1 and 3)
Analytically, we can know that the First Mover is not in motion (for everything in motion is moved by another - via the second premise). Yet, a thing can only be changeless if it is timeless (time is a measurement of change) and immaterial (every physical body is capable of being moved). The First Mover is also enormously powerful, since it is the cause of the universe's motion.
Now, there is an even more obvious way to express the third premise:
3*. The universe is in motion. (Premise)
This revised third premise is often subjected to the charge of a composition fallacy. The whole is not always like its parts. If every part of a floor is small, it doesn't follow that the floor as a whole is small.
However, there are instances in which the whole clearly is like its parts. For example, if every part of the floor is made of wood, then the floor as a whole is made of wood. So, which of these categories does the universe's motion fall under.
In order for the composition fallacy objection to work, it would have to be the case that everything in the universe is in motion, but that the universe as a whole is not in motion. But, surely this doesn't make any sense. For any interrelated whole that is composed of parts that are all in motion, the whole itself must also be in motion. It doesn't make sense to say the each of a train's parts is in motion, but that the train itself isn't in motion. In fact, the train itself must be in motion simply by virtue of the fact that all of its parts are in motion.
It seems clear, then, that the universe as a whole is in motion. This means that the universe's motion must be actualized by some external cause. This external cause is ultimately the First Mover. For, the universe just is the totality of all physical space, time, matter and energy. Therefore, the universe's mover must transcend physical space, time, matter and energy.
An additional objection often made is that in order for a thing X to be the cause of Y's motion, X must also be in motion. However, this objection is flawed for at least two reasons. First, X may move Y passively. For instance, one may be moved or changed upon the vision of a beautiful painting. It's not that someone is moved by virtue of the painting's motion, for the painting isn't actively doing anything. This is how Aristotle viewed the First Mover. The First Mover causes everything else to be in motion, but only by way of passivity.
However, this isn't my perspective. I believe that the First Mover (God) is more than a passive cause. The position that I adopt is that X need only be in motion to move Y if X is itself is already an entity subject to motion. Why, for instance, could an entity that transcends all motion not be the active cause of motion, and simply will motion eternally and without change? I have never read or heard a convincing argument against this hypothesis.