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How does Aquinasās Third Way argue from contingency to a necessary being?
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Thomism
St. Thomas Aquinas Enthroned Between the Doctors of the Old and New Testaments, with Personifications of the Virtues, Sciences, and Liberal Arts, fresco by Andrea da Firenze, c. 1365; in the Spanish Chapel of the Church of Santa Maria Novella, Florence.
In his Third Way, St. Thomas Aquinas argues for the existence of God by distinguishing between "possible" (contingent) beings and "necessary" beings.1
His argument proceeds as follows:
- Contingency: Possible beings are those capable of existing or not existing, often subject to generation and corruption. If a being is capable of not existing, there must be a time when it does not exist.1
- The Impossibility of Infinite Contingency: If every being were merely possible, there would have been a time when nothing existed. However, nothing can come into existence except through a being that already exists; therefore, if there were ever a time when nothing existed, nothing would exist now.1
- The Necessity of a Necessary Being: Because things do exist, there must be at least one necessary beingāa being that is not capable of not existing.1
- Conclusion: Since there cannot be an infinite chain of necessary beings whose necessity is caused by another, there must ultimately be a being that is necessary in itself, which Aquinas identifies as God.1