The general intention of this paper is to highlight the Platonic and Neoplatonic
themes that are explicit and implicit in Thomas’ discussion of the unity of being and the
good and the three fundamental precepts of the natural law. The Platonic themes I
concentrate on are participation, the unity of being and good, and the three principles of
Being, Life, and Intellect. I attend to these themes because scholars who treat Aquinas’
conception of the natural law tend to emphasize his debt to Aristotle rather than to the
Platonists. Yet the Platonists incontestably had a great influence on Thomas Aquinas’
Aquinas, we must remember, had the Neoplatonic texts of the
Liber de Causis, Proclus’ Elements of Theology
, Dionysius’ The Divine Names, and the
Theology of Aristotle. Thomas also indirectly encountered Platonic philosophy through
Augustine and Boethius, two of the main transmitters of Platonism, and the Arabic
authors Avicenna, Averroes, and Maimonides. While my approach is not fundamentally
at odds with scholars who see mostly Aristotle in Aquinas, I argue that being attentive to
the Platonic aspects of Aquinas helps us see how he unifies the human person with the
whole of being through the natural law. In addition, it is my hope that this paper will
contribute to clarifying three issues in the secondary literature: (a) outlining how being
and the good are one and the same in reality,
(b) showing that the natural law is based on
4
For a compelling treatment of Aquinas’ Neoplatonism see Wayne J. Hankey, God in Himself, Aquinas'
Doctrine of God as Expounded in the Summa Theologiae (Oxford: Oxford University Press, 1987). Also
see Wayne J. Hankey, "Aquinas' First Principle, Being or Unity?," Dionysius 4 (1980).
5
Thos. M. Johnson indicates that William of Morebeke finished translating Proclus’ Elements of Theology
from Greek into Latin on May 18
th
1268. Thos. M. Johnson, Proclus Metaphysical Elements, trans. Thos.
M. Johnson (Osceola: The Platonist, 1909). Footnote 10.
6
For instance, Pamela M. Hall and Ralph MacInerny argue that the natural law is based upon nature, and
accordingly does not consist of a set of practical principles of value distinct from being. I want to contribute
to the argument that “values” can be logically derived from “facts” by clearly and briefly laying out how
Thomas converts “being” and the “good”. See Pamela M. Hall, Narrative and the Natural Law: An
Interpretation of Thomistic Ethics (South Bend: University of Notre Dame Press, 1994). See also
McInerny’s response to Finnis and Grisez in Ralph McInerny, "The Principles of Natural Law," The
American Journal of Jurisprudence 25 (1980). While Grisez and other new natural law theorists maintain
that the natural law is metaphysically based on nature, they argue that epistemologically it is illicit to
logically derive the first principles of the good from metaphysical truths. Moreover, Grisez argues that
“Some interpreters mistakenly ask whether the word ‘good’ in the first principle [of the natural law] has a
4
Convention