Aquinas' Third Way: Contingency

Formulation

1. Whatever is contingent could have been different or not existed at all.
2. If everything were contingent, then there would be a time when nothing existed.
3. If there were a time when nothing existed, then nothing would exist now.
4. But things do exist now.
5. Therefore, not everything is contingent. (2, 3)
6. Therefore, there must be a necessary being.
7. This necessary being either derives its necessity from another necessary being, or is necessary in itself.
8. There cannot be an infinite regress of necessary beings.
9. Therefore, there must be a necessary being that is necessary in itself (God). (7, 8)

This is also pretty similar to the First Way and the Second Way, but instead of focusing on motion or causation, it focuses on contingency.

Contingency and the The First Premise

The argument is based on the distinction between necessary and contingent beings. Necessary beings are beings that must exist for logical reasons, and contingent beings are beings that could have been different or not existed at all, and still be logically consistent.

There's one issue in the first premise, and this can be seen by comparing the following two statements:

1. Definition - Contingent beings can fail to exist.
2. Premise 1 - Contingent beings failed to exist at some point.

Being "able" to fail to exist is not the same as actually failing to exist. The being could have been present eternally, but still be contingent.

An alternative interpretation is that contingent beings have a natural tendency towards decay and non-existence. The problem is that this still does not imply that they actually failed to exist at some point.

While an object could tend towards decay, it must have certain manifestation conditions in order to decay. For instance, a glass of water could decay (evaporate), but only given certain conditions, like the pressure difference and temperature.

Contingency of the Universe, a Fallacy of Composition

The argument also seems to commit a fallacy of composition. It states that if everything in the universe is contingent, then the universe itself is contingent.

This is not necessarily true. Consider the following analogy:

1. All atoms are invisible.
2. Therefore, everything made of atoms is invisible.

More formally speaking, this fallacy of composition can be written as:

Where is the universe, is the contingency of , and is the contingency of the universe.

Contingency and the Second Premise

The second premise is that if everything were contingent, then there would be a time when nothing existed. We shall grant the first premise for the sake of argument, and focus on the second premise.

Let be a contingent being that exists at time and stops existing at time . Let be another contingent being that starts existing at time and stops existing at time , and so on.

Generally, starts existing at time and stops existing at time .

This scenario fits the first premise: each did not exist at some point. However, the second premise does not hold, because there is always something that exists at any given time. There's always some at any time in .

In other words, .

As such, even if we grant Premise 1 (which is already problematic), Premise 2 does not necessarily follow.

The Necessary Being

The conclusion of the argument is that there must be a necessary being. As previously stated, arguments like this does not necessarily lead to the traditional conception of God.

Individuals can accept many other forms of necessary beings as the conclusion, including:

• Something within the universe that is necessary, like quantum fields, universal wavefunctions, the fundamental particles, and so on.
• The universe itself being necessary.
• Something outside the universe that is necessary, but not God; like an impersonal and neo-Platonic principle.