Aquinas' Five Ways: The Third Way, Possibility and Necessity

     The last three ways may be better to cover one at a time, so we have the space to do it properly. The third way is from possibility and necessity. The things in our experience are only possible, but not necessary, like a chair. The chair can exist, but it doesn’t have to exist. At one time it didn’t exist, and then something caused it to exist, and at some point it will stop existing. If everything were only possible, then there could have been a point in which nothing existed. If this happened then nothing would exist now, since nothing can come from nothing. Obviously, things do exist. The alternative is that some things are necessary and must exist, and are not just possible. Logically, they must receive their necessity from themselves or from something else, and we’ve already seen that a chain of causes cannot go on for infinity.  Therefore, there must be something that does not depend on anything else for its existence, but is necessary of itself. This all men speak of as God. 

​     This is the hardest of the five ways for me to wrap my mind around. I think it’s because all of the things around us are only possible, so it’s hard to imagine that something could be truly necessary. We may think of the universe as necessary, but it began to exist with the Big Bang. Even the laws of the universe are not necessary as many of them began to exist with the Big Bang, and they don’t truly have to be what they are. God, however, is completely self-sufficient and has created everything else that exists. 

     I think what St. Thomas Aquinas wants us to see is that must things depend on other things to exist. We call this contingent existence. God, on the other hand, is necessary. He is pure existence or the act of existence itself, and He is holding everything else in existence at every moment. Last week I used the example of a pool cue striking a cue ball which then strikes the other balls. This is a series of causes and effects that follow in a sequence. Some things have effects that happen at exactly the same moment. For example, when you plug a lamp into a power outlet the electricity causes the lamp to light up, but it happens simultaneously. The same thing happens when you pick up a ball. You hand is causes the ball to rise, but it’s not one thing and then the other, they happen at the same time. God didn’t just create us and let us go; like a parent, He is constantly holding us in existence. The Catechism says:

“With creation, God does not abandon his creatures to themselves. He not only gives them being and existence, but also, and at every moment, upholds and sustains them in being, enables them to act and brings them to their final end. Recognizing this utter dependence with respect to the Creator is a source of wisdom and freedom, of joy and confidence” (CCC 301).

     And as the Acts of the Apostles says, “For in him we live, and move, and have our being” (Acts 17:28)