What is the weakness of Thomas Aquinas's unmoved mover?

Answer 1

Aquinas' First Way, the argument for an unmoved mover ("move" in Aquinas' day means both moving and/or changing), proceeds as follows:

1. Some things are changing

2. Everything being changed is changed by something outside itself

3. Either there is a first changer or nothing is being changed

4. There is a first changer

Keep in mind that this argument is not for an unmoved mover in the past, but into deeper levels of reality at the present.

Essentially, it says that if something is changing (or moving), it can only do so because something external to itself is forcing it to. And that something has something external forcing it, and so on.

For example, the dog's leg does not move by itself, but only because muscles move the leg. But the muscles don't move by themselves, but only because neurons are firing. But neurons do not fire by themselves, but only because electrons are forcing them to, and so on.

If you can imagine a caboose that is moving, you know the caboose doesn't have an engine and that the reason it's moving is because it is being pulled by a boxcar. But you know that boxcar is not moving by itself, but is being pulled by another boxcar. And so on.

And you know that somewhere down the line there must be a train engine, otherwise the caboose would not move at all.

Likewise, somewhere in a deep and more fundamental level of reality there must be something that is changing everything else that is itself not being changed by another: an unmoved mover.

Problems

One of the main problems with it is Newton's first law: that which is in motion tends to remain in motion. I.e., things in motion without friction are not being moved by another.