The Five Ways and God's Existence: The Third Way

So, after examining Aquinas's first and second proofs for God's existence, let us take a thorough investigation into his third way which concerns contingent beings. First, what is a contingent being? What does it mean to be contingent? The Merriam-Webster Online Dictionary defines being 'contingent' as being "dependent on or conditioned by something else." This third way Thomas offers builds on the previous two, showing how we can know that there must exist a being who has to exist, what we call a 'necessary being'. This non-contingent being has to exist in order for beings who have the possibility not to exist to exist at all.

We know that we humans, the Earth itself, and the Universe as a whole do not have to exist and indeed did not exist at all at a given point. In fact, we see things go in and out of existence all around us. People are born, people die. Trees grow, trees die. These beings are what we call 'contingent beings'. They don't have to exist in the first place. No contingent beings do, by definition. They have the possibility of either existing or not existing. Both are potentialities for them.

So, we see that in order for contingent beings to begin to exist and to remain in existence, there's needs to be some being that is not contingent or dependent upon anything for its own existence. This being must needs be existence itself and must have to exist by its very nature and essence. It must be pure being.

Now, we must note a very important, logical principle that has been alluded to in previous posts, namely, nothing gives what it does not have. We could word this principle in another way: From nothing, nothing is able to come. Both of these principles of reason are self-evident and should be readily understood by all. So, to apply these principles to our current study of contingent beings and existence, we see that if everything in existence has the potential for non-being, including the universe as a whole, nothing would exist right now or ever. If the universe popped into existence at a given point, we must necessarily trace all beings back to that one point before the universe's existence was actualized, namely, the point when nothing existed. However, as we just saw, nothing comes from nothing. No being, no actuality can come from non-being or non-actuality. This is an undeniable impossibility. 

And so, we must ask ourselves whether or not it is possible for contingent beings to just go back into the past in an infinite regress. The clear answer is no. The necessity of a given being is caused by another, as we saw in the previous ways of Aquinas. However, we simply cannot go back into infinity with an endless series of contingent beings all causing each other to have being and thus exist. Just as you can't have an endless series of boxcars all causing each other to go from potential movement to actual movement without the locomotive, we can't have it that contingent, unnecessary beings all cause each other to have existence and actuality. As Aquinas writes, "Therefore we cannot but postulate the existence of some being having of itself its own necessity, and not receiving it from another, but rather causing in others their necessity. This all men speak of as God."

So, to conclude this post, we see that God, the First Mover and Necessary Being, I AM WHO AM, must exist in order for all contingent beings (like ourselves) to exist at all. This One Being we call God gives rise to all other beings and holds them in existence. This is the Third Way of Thomas Aquinas.