1265–1273 · Thomas Aquinas, Summa Theologica II-II, q. 175, a. 3, ad 4
In another way the third heaven may signify a supra-mundane vision. Such a vision may be called the third heaven in three ways. First, according to the order of the cognitive powers. In this way the first heaven would indicate a supramundane bodily vision, conveyed through the senses; thus was seen the hand of one writing on the wall (Dan. 5:5); the second heaven would be an imaginary vision such as Isaias saw, and John in the Apocalypse; and the third heaven would denote an intellectual vision according to Augustine's explanation (Gen. ad lit. xii, 26,28,34). Secondly, the third heaven may be taken according to the order of things knowable, the first heaven being "the knowledge of heavenly bodies, the second the knowledge of heavenly spirits, the third the knowledge of God Himself." Thirdly, the third heaven may denote the contemplation of God according to the degrees of knowledge whereby God is seen. The first of these degrees belongs to the angels of the lowest hierarchy [*Cf. FP, Q[108], A[1]], the second to the angels of the middle hierarchy, the third to the angels of the highest hierarchy, according to the gloss on 2 Cor. 12. And since the vision of God cannot be without delight, he says that he was not only "rapt to the third heaven" by reason of his contemplation, but also into "Paradise" by reason of the consequent delight.