The doctrine of analogy requires that when theologians describe God with a term that usually applies to created reality, they negate some aspects of the usual meaning of the term but affirm and purify other aspects. The divine attributes help identify which aspects of the term “generation” and “procession” or “spiration” in their created sense do not apply to the Godhead. This methodology has been consistently deployed throughout the history of trinitarian thought, providing increasing clarity concerning the divine processions, especially as early, implicit use of the doctrine of analogy was replaced by a conscious awareness of the doctrine in all its complexities. When restricted in accordance with this method, the meaning of “generation” provides a reason to affirm the pro-Nicene position over alternatives such as those found in Arius.

D. Glenn Butner Jr., Trinitarian Dogmatics, 52.

The doctrine of analogy helps Aquinas more clearly differentiate generation from creation by clarifying the relationship between God and the world. Aquinas recognizes that when humans use words to speak of God, they use words they have learned “as they are in creatures.” These creatures have attributes as they have received them from God, their cause. One implication is that, properly speaking, these attributes must fully belong to God and only secondarily to creatures, who have these attributes by participation. However, in our theological language, the terms primarily signify created realities perceived by the human mind and signify God only in a secondary and analogical sense . . . Analogy does not tell us which words to use of God, but once the right words are determined, the doctrine of analogy helps us to use these words precisely. As Brian Davies summarizes, “Any talk of procession in God must be understood in a way that prevents us from attributing to him anything essentially creaturely.”

D. Glenn Butner Jr., Trinitarian Dogmatics, 56-57.