Aquinas' Five Ways

Third Way

Argument from Necessity

Contents

Outline


Explanation


Objections


Sources

Argument from Necessity: Outline

Aquinas' third way rests on the distinction between necessary and contingent beings. Most things, if not everything, is considered to be a contingent being. Contingent beings are beings that are allowed to not exist. In other words, a particular contingent being could stop existing without detriment to the existence of other contingent things. Any one of us could stop existing at any moment, but that doesn't have any impact on the existence of other people, buildings, galaxies, etc. Another facet of contingent beings is that there was a time they did not exist. There was a time that none of us existed, yet the world still continued normally. A necessary being, on the other hand, is something that must exist for all time.


  • We perceive the existence of contingent beings
  • For each contingent being, there was a time it did not exist
  • If all beings were contingent, there must've been a time where nothing existed
  • If nothing existed, nothing could bring the other contingent beings into existence
  • If this were true, nothing would currently exist
  • Therefore, at least one thing must exist out of its own necessity and does not derive its existence from another being
  • We all this necessary being God


Argument from Necessity: Explained

Imagine an infinite, straight line that's meant to represent time. Now imagine that above this line is a number of dots, each dot representing the existence of an object in the universe. While at first glance there may appear to be a large number of dots along the line, in truth, most of the line should be empty. The universe only has a finite number of objects in it, and the line representing time is infinite. Since objects would exist very little of the time, the existence of things seems improbable. Consequently, all things in existence should be dependent on something necessary given the improbability of their existence. Such a necessary being would be what we call God.



Objections

Fallacy of Composition with Contingency

It may be true that everything in existence is contingent, finite, limited, but why must we conclude that everything as a whole is also limited? Take, for example, the human race. The human lifespan may be finite, but the human civilization as a whole isn't finite for the sole reason that humans have a limited lifespan. If humanity was to go extinct, it would be due to other factors, not its contingency. The same thought process can be applied to the universe. In addition, contingent beings that cease to exist don't just simply disappear. The termination of a contingent being often generates something else. An explosion of a star creates a black hole. A dead body can be harvested for energy by other organisms.