Aquinas' Argument for the Identity of Divine Essence and Existence, In Syllogistic Format

Aquinas' Argument for the Identity of Divine Essence and Existence, In Syllogistic Format

From St. Thomas Aquinas, Summa theologiae I.3.4c:

A. The Text: "First, whatever a thing has besides its essence must be caused either by the constituent principles of that essence (like a property that necessarily accompanies the species--as the faculty of laughing is proper to a man--and is caused by the constituent principles of the species), or by some exterior agent--as heat is caused in water by fire. Therefore, if the existence of a thing differs from its essence, this existence must be caused either by some exterior agent or by its essential principles. Now it is impossible for a thing's existence to be caused by its essential constituent principles, for nothing can be the sufficient cause of its own existence, if its existence is caused. Therefore that thing, whose existence differs from its essence, must have its existence caused by another. But this cannot be true of God; because we call God the first efficient cause. Therefore it is impossible that in God His existence should differ from His essence."

B. The Argument in Syllogistic Format:

Part One: 

Major: Whatever a thing has besides its essence must be caused either by the constituent principles of that essence, or by some exterior agent.

Minor: The existence of some things is besides their essence. (Because some things cease to be.)

Conclusion: Therefore, the existence of those things whose existence differs from their essence must be caused either by some exterior agent or by their essential principles. 

Part Two:

Major: The existence of those things whose existence differs from its essence must be caused either by some exterior agent or by their essential principles (= Conclusion of Part One). 

Minor: It is impossible for a thing's existence to be caused by its essential constituent principles. (Nothing can be the sufficient cause of its own existence.)

Conclusion: Therefore that thing whose existence differs from its essence must have its existence caused by another. 

Part Three: 

Major: That thing whose existence differs from its essence must have its existence caused by another (= Conclusion of Part Two). 

Minor: But God's existence is not caused by another (because we call God the first efficient cause; cf. ST I.2.3). 

Conclusion: Therefore it is impossible that in God His existence should differ from His essence.