The classical philosophical tradition beginning with Pythagoras, Plato and Aristotle considered beauty to be a divine ideal, a reflection of goodness exemplified most of all by the principle of proportion. The Neoplatonic reinterpretation of the classical tradition, especially by the Church Father Dionysius the Areopagite, recognized beauty as a property or “name” of God. However, in the metaphysical system of St. Thomas Aquinas, who recognized being or existence as the highest and most fundamental act of all things, with God understood as the “mysterious positive fullness of perfection, the unlimited fullness of existence itself,” beauty became a transcendental or universal property of being, analogously expressed in all real things. Through an exploration of the Thomistic understanding of beauty and proportion, the role of both in the art and philosophy of the Middle Ages can be brought to light.
St. Thomas Aquinas founded all of his philosophical and theological teachings on being as the source from which all things exist and have their perfections. Two of the most important concepts in his explication of this teaching are analogous participation and the transcendental properties of being. Since nothing that exists is self-sufficient in itself but receives its existence from others and within certain conditional parameters, St. Thomas understood that no finite thing possesses being absolutely, but only as essence, “a limited mode of participation in the unlimited fullness of pure existence itself”, derived from an ultimate source who is the infinity of being and perfection with no derivation or division, namely God. From this, he further explained that being is not held univocally or in the same way by all things, much less by God and his creatures, but rather by proportionate analogy, with all created things authentically participating in the infinite being of God but doing so in diverse ways, unique to their particular nature and individuality. Because being is also “the root of all perfection” that can exist in things, St. Thomas recognized the transcendental properties of being, which Fr. W. Norris Clarke lists as truth, goodness, beauty, unity and activity (as opposed to potency), exhibited by all things that really exist. However, like all perfections, these properties are not identical in creatures but rather are analogous, with some things being more or less true, good, beautiful, etc. than others insofar as they more or less participate in being within the overall hierarchy of existence.
All of these transcendental properties express aspects of being which between themselves and in God are ultimately convertible with one another, yet to our limited intellects they are distinguishable, and so truth represents the intrinsic intelligibility or intentional coherence of being in relation to intellects, goodness the intrinsic desirability and fittingness of being, etc. Beauty is unique among the properties in that it is a kind of “synthesis of all the transcendentals,” a splendor or brilliance radiating the divine source of being which “adds to goodness ordination to cognitive power”, both through the senses and intellect; in this way, “beauty is being insofar as its contemplation gives delight.” As embodied spirits or rational animals, humans “cannot perceive beauty—it cannot shine out to us and give us delight—except as embodied in some sensory embodiment or symbol” through the “likeness of the divine beauty, participated in by created things.” While the intellect can unveil the dependence of all things on God as their ultimate cause and principle of sustenance through metaphysical arguments, beauty can also be a pathway to God through final causality, based in the specific natures of all beings which orient their actions toward the achievement of perfection available to them. Through proportion, beauty discovers the echoes of final causality and traces them to their source in God, who calls all things to himself as their ultimate fulfillment.
St. Thomas assigned proportion as one of three qualifications of beauty, alongside integrity and clarity. While integrity derives from the perfection of a thing in its specific identity and wholeness (unity), and clarity consists in “the splendor of existence shining forth through form in creatures” (truth), proportion is founded on final causality (goodness). Considered as consonance or harmony, proportion is the interconnection of the contrary parts of a composite, material being within itself, with all of its constituent elements harmonized by the perfection of its form, or, for immaterial beings such as God and angels, the intrinsic harmony of integrity and clarity within their simple natures. Proportion in created things is not only found in the natural harmony of each individual, but also in the consonance of all beings connected to one another. For this reason, the ancient Greek word for beauty (kalos) is derived from the word for “the act of calling” (kaleo): beauty subsists in the eminent and transcendent vocation of created things toward God, the source of their being and perfection.
In medieval aesthetics, particularly that of the Schoolmen, the fine arts were not clearly distinguished from the concept of art in general, which “operates for the good of the work done” and is based in the intellect working to invent and contemplate what Etienne Gilson calls “germinal forms”. In this way, anything which was first conceived in the mind and then implemented in the exterior world, whether in skills, crafts or what would in Renaissance humanism be considered the fine arts, was considered artistic. Nevertheless, even without the distinction of the fine arts from their relatives, medieval thinkers recognized beauty as the ultimate object of all the arts, including those considered to be more practical; as St. Thomas observes, “No one cares to fashion or represent anything except for its beauty.” For this reason, medieval society, especially with its guild economy, sought to produce the most excellent and beautiful objects it could rather than mass production in the vein of industrial utilitarianism. Even objects of ordinary use were held to high standards of quality, and activities requiring great discipline to achieve a perfection of operation, including pragmatic skills, were seen as habitus perfecting the people who made or performed them and edifying those who received them. This view of art and beauty was also extended to sacred art, with Abbot Suger seeking the highest expression of integral perfection in his Gothic architecture, the Limbourg brothers and Giotto applying radiance to the bright colorations of their paintings and the composers of Gregorian and polyphonic chant exemplifying proportion in the numinous harmony of their compositions as an imitation of the choir of angels in Heaven, as well as St. Thomas and the scholastics who achieved beauty in the systematic harmony and brilliance of their summae.
In light of the aesthetics of St. Thomas Aquinas and the medieval artistic tradition, proportion becomes not only a standard for art or a characteristic of beauty but a kind of mystical expression, with the pursuit of beauty perfecting the intellect and raising it up to the contemplation of God, who creates all things through his beauty, via the discovery and celebration of the vocative return to God within and between all things. In this way, proportion and its explication by philosophy and the arts acts as a preview or sacramental sign of the Beatific Vision, “the ultimate end of man” in which our intellects will behold the very essence of God in Heaven, perceiving in him the finality of all things. Whereas the pursuit of truth consists in the conformity of the mind to the reality of God and the love of the good is fulfilled through unity with that which is real, the contemplation of beauty conforms the whole person to God in the perfection of his divinity.
In conclusion, the aesthetics of medieval philosophy and particularly of St. Thomas Aquinas transforms the arts, both fine and practical, into avenues of perfection in virtue. They also become evangelical and sanctifying, mystically pointing to the beauty of God by highlighting the proportion of all things to him as their final cause and thereby counteracting evil by reorienting things toward their proper intention and fulfillment in divine beauty. Grounded in the objectivity of being and its transcendental properties, a Thomistic theory of beauty thus elevates art beyond the merely sensual, expressive or utilitarian, holding it up to standards of truth, goodness and finality which can restore its place as an indispensable path for the cultivation of the mind, the perfection of the person and the renewal of culture.
 Aiste Celkyte, “Ancient Aesthetics,” in Internet Encyclopedia of Philosophy, at www.iep.utm.edu.
 Dionysius the Areopagite, “Divine Names,” in The Collected Works of Dionysius the Areopagite, trans. John Parker (Devoted Publishing, 2015), 20. Kindle.
 W. Norris Clarke, The One and the Many (Notre Dame, Indiana: University of Notre Dame Press, 2001), 289. Kindle.
 Clarke, The One, 162.
 Thomas Aquinas, An Introduction to the Metaphysics of St. Thomas Aquinas, trans. James F. Anderson (Washington, DC: Regnery Publishing, 1953), 37.
 Clarke, The One, 334.
 Clarke, The One, 361.
 Jacques Maritain, A Preface to Metaphysics (London: Sheed & Ward, 1943), 1104. Kindle.
 Clarke, The One, 372.
 Thomas Aquinas, An Introduction, 95.
 Clarke, The One, 363.
 Clarke, The One, 371.
 Thomas Aquinas, De divinis nominibus, chapter 4, lecture 5, quoted in Francis Selman, Aquinas 101 (Notre Dame, Indiana: Ave Maria, 2007), 54.
 Thomas Aquinas, An Introduction, 89.
 Thomas Aquinas, Summa theologiae, I, q. 39, a. 8, at New Advent, www.newadvent.org.
 Clarke, The One, 373.
 Thomas Aquinas, An Introduction, 97.
 Thomas Aquinas, An Introduction, 91.
 Jacques Maritain, Art and Scholasticism, 2nd ed. (Providence, RI: Cluny, 2020), 15.
 Etienne Gilson, Painting and Reality (Cleveland, Ohio: Meridian, 1961), 150.
 Aquinas, De divinis, chapter 4, lecture 5.
 Maritain, Art, 12.
 Clarke, The One, 372.
 Thomas Aquinas, An Introduction, 93-95.
 Gilson, Painting, 179.
 Maritain, Art, 49.