To All: Detailed pickings of Aquinas' First Way #2: Aristotle's Solution to Parmenides

NOTE: THIS IS LESS OF A DEBATE THREAD AND MORE OF AN EXPLANATORY THREAD, FOR EASY LATER REFERENCE. THE AIM OF THIS THREAD IS TO GIVE READERS PROPER UNDERSTANDING OF THE ARGUMENT, NOT NECESSARILY TO DEBATE ITS TRUTH VALUE.

Act and Potency

In the first part, we saw that Parmenides divided the world into being and non-being, and as a result of that, change is impossible. Aristotle thought that it was clear that things do change, and he provided the solution by further dividing being (or existence) into two: actuality and potentiality.

Actuality is full being, or existence. An actual bowl of water, for example. Potentiality is the way the water could be: ice, steam, vapor, gas, moved to the left, moved to the right, on the floor, and so on. So potentiality serves as a sort of midway ground between being and non-being. Note that for Aristotle, a potentiality is rooted in what the thing can actually become. On this view, the water is not potentially on fire, or potentially a snake. There is a specific range of states the water is potentially in.

When actual liquid water (potential ice) becomes actual ice, it then becomes potentially liquid water. So the two states of being can swap places like that, between actual and potential.

For a potential to become actual, something else must make it actual

A potential is only potential, and not actual. Therefore, it has no causal power and thus no ability to make itself actual. Potential ice (actual liquid water) cannot make your drink cold. Only actual ice can. Liquid water that is potentially on the floor cannot make itself actually on the floor. It requires someone or something that is ACTUAL to push it there.

So this provided an answer to Parmenides. Change is possible because of the act/potency distinction.

Parmenides in Retrospect

Now hopefully you can see more clearly what Parmenides was saying in hindsight, when he made the distinction between being and non-being. He was saying that anything is either fully actual (existence/being), or it doesn't exist at all. No change can happen in such a world. He failed to divide being/existence into actual and potential, which is what is required for change to occur.

This Concludes #2

The take-home point is that Aristotle divided the world into three instead of just two, in order to provide an answer to Parmenides: actuality (or being, or existence), potentiality (midway ground), and non-being. And for a potential to become actual requires something else (something that is actual) to make it actual.

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