St. Thomas Aquinas' third way is the Argument from Possibility and Necessity, or the Reductio argument. It's based on the observation that things exist and don't need to exist.

Things Fall Apart

Lets start, as St. Thomas Aquinas does, with our everyday experience.  Things corrupt; they fall apart.  Also, things come into being -- babies are born, plants grow, buildings are built.  We create things - crafts, projects, companies - and they will eventually break or fail. Things come into being, and they go out of being.

Nothing Lasts Forever
 
Next, let's consider the expression you've likely heard of, that "nothing lasts forever".  Why doesn't it?

Well, what is "forever"?  Forever is infinite time. Infinite time is all the time you need for anything. That project you'd do if you just had more time? No problem, if you have forever. In fact, infinite time is all the time you need for everything. Because once you're done, there's still more time.

Infinite time is enough time for everything to happen. Every single thing that could happen, in every combination it could happen in.  Want to flip a coin and get 100 heads in a row?  If you have forever, you'll get it eventually.  Bowl a perfect game? Find a needle in a haystack? Find a pair of shoes that feels good and looks good?  You'll get it done if you have forever.

If everything can end and you have forever, then everything will end.  If there has been infinite time -- no beginning -- then there has been enough time for every possibility to happen.  One of those possibilities is that everything would end.

Let's summarize this point:

• If it's possible that everything could end - everything, simultaneously,
• and you have infinite time,
• then "everything ending" must have already happened.

You Can't Get Something for Nothing

If everything ended at some point - everything, period - then what would have come next?  Nothing.  Nothing comes from nothing.  If everything stopped, there would be nothing left to start again.

If I remove one domino from a line of them, the others could still be knocked over.  You could reach in and tap the next one.  But what if I take all the dominoes away?  No more will ever be lined up and knocked over.  The whole thing is over.

I'm Not Dead Yet

Something is here, though.  You're here reading. I'm here. Your computer or phone is here. You're breathing air.  Things are happening all around.

What does that mean?  It means that something is wrong with this argument:

• If it's possible that everything could end - everything, simultaneously,
• and you have infinite time,
• then "everything ending" must have already happened.

What could be wrong? The second point could be the problem. Maybe there isn't infinite time. (Physics and cosmology currently point that way.) In this case, there was a beginning. If there was a beginning, then we go to the form of the Argument from Contingency that deals with the Beginning of Existence.

The first point could be the problem, too. What if not every thing has a beginning and end? If there is something without a beginning and end, then it wouldn't end, even with infinite time. Even if we reject the argument from the Beginning of Existence, we're caught by this argument. Without a beginning, there still must be something timeless keeping things going. We call that God.


We're still considering arguments for God from contingency. The last one, coming next, is an argument from degree.

Need a review first? Dr. Peter Kreeft teaches the first three "ways" we've covered in The Thomistic Cosmological Argument. You can also read St. Thomas Aquinas' own formulation at http://www.newadvent.org/summa/1002.htm