The Five Ways: Aquinas's Arguments for the Existence of God

1. The Argument from Motion

Starting Point: We observe that things in the world are in motion. The presence of changing realities is undeniable.

• Step 2: Applying the principle of causality, everything that is moved must be moved by another. Nothing can be brought from potentiality to actuality except by something already in a state of act.
• Step 3: It is impossible to proceed to infinity in the series of moved movers. If everything were moved by another, there would be no first mover.
• Conclusion: Since things are currently moving, there must be a First Unmoved Mover, which we call God.

2. The Argument from Efficient Causality

Starting Point: We experience a world governed by an order of efficient causes.

• Step 2: Applying the principle of causality, a thing cannot be the efficient cause of itself.
• Step 3: It is impossible to have an infinite series of efficient causes, as there must be a first cause to produce subsequent effects.
• Conclusion: There must be a First Efficient Cause, which we call God.

3. The Argument from Contingency

Starting Point: We observe that beings in the world are contingent; they exist but have the potential not to exist.

• Step 2: If all beings were merely contingent, there would have been a time when nothing existed.
• Step 3: If at one time nothing existed, nothing could exist now. Since things clearly exist, not everything can be contingent.
• Conclusion: There must be a Necessary Being that causes the existence of all other beings, which we call God.

4. The Argument from Degrees of Perfection

Starting Point: We observe degrees of perfection in the world. We find that some things are more good, true, and noble than others.

• Step 2: To possess a greater or lesser degree of perfection implies a comparison to a maximum standard.
• Step 3: That which is the maximum in any genus is the cause of all in that genus.
• Conclusion: There must be a source of all perfections, which we call God.

5. The Argument from Finality

Starting Point: We observe order in the universe. Natural bodies that lack knowledge act toward an end to obtain the best result, rather than by pure chance.

• Step 2: Things that lack knowledge do not tend toward an end unless directed by an intelligent being.
• Step 3: We cannot accept an indefinite series of guiding intelligences.
• Conclusion: There must exist a Supreme Intelligence that directs all things toward their end, which we call God.