Notes on Finality in Aquinas’s Fifth Way

Abstract Aquinas’s Fifth Way argues for God’s existence from the perception of goal-directed activity in nature. Its details are difficult to understand. This study interprets the premises and offers background reasoning for them, which Aquinas develops elsewhere in his writings. A major focus is clarifying the scope of finality the Fifth Way invokes. The argument leaves unspecified the kinds of purposive activity in nature Aquinas has in mind. Thus, the discussion first treats types of purposive activity in nature Aquinas recognizes. It then looks at the two reasons the argument gives for final causes in nature. Things tend to act in regular ways and tend toward what is ‘best’. Attention then turns to the key premise that goal-directed activity in nonrational beings requires direction by something with intelligence. A final section of the article explores why Aquinas seems to look to a single source of finality in nature and why, in the conclusion, he claims that we call this God. Thus, Aquinas’s larger views on finality in nature shed light on his intents in the Fifth Way.