PHL100: Aquinas's Five Arguments
Introduction
Aquinas's Five Arguments for the Existence of God
Here is just one way to sketch out Aquinas's arguments.
- Motion
- There are things in motion.
- Things are only actually in motion if they can potentially
be in motion, and if something actually moving pushes them.
- A thing can have a potential and an actuality, but not both
at the same time. Something can potentially move, or actually move,
but not both.
- Thus, nothing can push itself. Each thing in motion moved
by something else in motion prior to it.
- [Implicit premise: time is linear.]
- This chain cannot go back forever.
- There must have been a first mover.
- Cause
- There are causes and effects.
- Each effect has a cause.
- An effect cannot be its own cause.
- Thus, each effect must have a prior and other cause.
- [Implicit premise: causal chains are linear.]
- This chain cannot go back forever.
- There must have been a first cause.
- Possibility and Necessity
- There are things which are possible: them come into and
out of being.
- By definition, nothing is possible but always existing
(here Aquinas seems to mean that possible is a temporal notion,
as noted above).
- Everything is merely possible, so everything could fail
to exist.
- There must have been one time when everything failed to
exist.
- But if there was a time when nothing existed, then there
would have been a time when nothing could exist (since nothing
can come from nothing).
- There must exist a necessary being.
- Gradition of Being
- Many (positive) properties come in degrees (some
people are more good than others, etc.)
- More and less are measured against some maximum.
- There must be something having the maximum properties (all
good, all knowing, all powerful).
- Governance of the World [The Design Argument]
- We see that even things without minds or
knowledge have goals.
- These goals are the best result.
- There must be a design of nature for this to occur.
- There must be a designer of nature.