Barring Aristotle, Pseudo-Dionysius was the fifth and sixth century theologian Thomas Aquinas quoted more frequently than any other writer through his extensive treatises. Surprisingly, very little attention has been paid to the role of Pseudo-Dionysius in the formation of Aquinas' philosophy. Fran O'Rourke, in Pseudo-Dionysius and the Metaphysics of Aquinas is the only author to investigate the pervasive influence of Dionysius' Neoplatonic thought on Aquinas, while examining the latter's profound originality.
O'Rourke discusses topics such as knowledge of the absolute, existence as the first and most universal perfection, the diffusion of creation, the hierarchy of creatures and their return to God as the final end. O'Rourke devotes special attention to the Neoplatonic elements present in Aquinas' thought, noting his emphasis on "being" as a particular degree of perfection or intensity. O'Rourke also considers the relation of being and goodness in light of Aquinas' nuanced reversal of Dionysius' theory on the primacy of good, and Aquinas' arguments for the transcendental nature of goodness.