In the 20th century, some prominent Thomists questioned whether St. Thomas Aquinas is really committed to a theory of divine ideas. There is no doubt that Aquinas articulates such a theory in his Sentences Commentary, Disputed Questions on Truth, and Summa theologiae. Still, he seems to omit an account of divine ideas in the Summa Contra Gentiles. If St. Thomas thinks divine ideas are necessary for understanding God's knowledge, why would he skip discussing them in this ex professo work? This paper will argue two points. First, St. Thomas does articulate a theory of divine ideas in the Summa Contra Gentiles, even though he changes his terminology. His account of divine reasons (rationes) is equivalent to a theory of divine ideas. Second, Aquinas changes his vocabulary because of the more apologetic aim of the work. Use of the term ‘ideas’ would be less effective in dialogue with his Muslim and pagan interlocutors.