Saint Thomas Aquinas on Virtue and Sin

Portrait of Saint Thomas Aquinas, 1476, by Carlo Crivelli. Ascoli Piceno, Italy. Public Domain

According to English philosopher Anthony Kenny, Saint Thomas Aquinas was “one of the dozen greatest philosophers of the Western world.” Not only was the 13th-century Dominican monk a superb writer and logician, he was also a gifted teacher and poet.

Throughout his writings, Aquinas articulated a cohesive Christian worldview wherein faith and reason complemented each other to create or allow an ethical life. His conception of virtue as a balance between extremes can help us see our flaws more clearly. It can also help steer our lives in the right direction.

Aquinas’s Inspiration: Aristotle on Human Nature

We can’t learn from Aquinas without first considering his favorite philosopher: Aristotle. The ancient Greek polymath asked three fundamental questions that shaped Aquinas’s thinking: Who am I? How should I live? Where am I going?

Aristotle answered these saying that “man is by nature a social animal” and that “man alone of the animals possesses speech.” “Speech” is the ability to reason, discern right from wrong, and use that knowledge to inform everyday life. We need to live according to reason in communities that foster our shared humanity. That’s necessary to reach our destination: eudaimonia.

Eudaimonia is often translated as “happiness” or “joy,” though it’s deeper than both. Literally, it means “having a good indwelling spirit.” It’s sustained bliss that combines emotional wellbeing and spiritual elation.

First page of a 1566 manuscript of Aristotle’s "Nicomachean Ethics," with Greek and Latin text. Public Domain

Aristotle admitted that eudaimonia is partly beyond our control. He thought that health, wealth, birthplace, and even physical attractiveness influence the extent to which we can attain it, though we can hardly choose how much of each to have in our life.

Nevertheless, the Greek philosopher was not a determinist. He believed in human agency. In “Nicomachean Ethics,” he outlined a map to cultivate specific virtues through constant and conscious effort.

Vice, Virtue, and the Golden Mean

For Aristotle, anything we do, from studying for a test to developing a relationship with a lifelong partner, implicitly aims at a good. All goods aim at eudaimonia. Since we’re rational beings, we can use reason to guide our pursuit of eudaimonia. We can become more conscious of our deeds and actively follow patterns that better align with virtue. To do so, Aristotle suggested we aim for the “golden mean.”

For example, we often face things that make us afraid. The virtue that helps us overcome fear is courage. When we have too little courage, we act in cowardly ways. We refuse to face our fear even though we should.

However, we could also have too much courage, which Aristotle called “rashness.” That’s when we ignore a fear we should heed, like choosing to stray from safe hiking paths in a remote wilderness.

Another example of a golden mean is “temperance.” On one extreme of temperance is “licentiousness”: the tendency to indulge in pleasures without restraint. Binge drinking is an example.

The other extreme is “insensibility”: the inability to enjoy the right pleasures in the right manner, at the right time. An example might be someone who is rigidly averse to the basic pleasures we derive from such essential needs as eating, drinking water, moving our body, and so forth.

"Triumph of St. Thomas Aquinas," 1471, by Benozzo Gozzoli. Tempera on panel; 90 1/2 inches by 40 1/8 inches. Louvre, Paris. The painting shows Aquinas between Plato and Aristotle. Public Domain

Be they excessive or defective, extremes preclude virtue. We can only act virtuously when we act close to the golden mean. To do so, we should apply reason to situations and choose the best course possible: Should we strive to overcome our fear, or is it better to heed its warnings; does the moment call for moderate enjoyment, or is restraint the better choice? The more we act according to reason, the more we align with virtue.

Aquinas on Virtue and Sin

At the University of Naples, Aquinas first read Aristotle’s “Nicomachean Ethics.”  He later spent much of his professional career trying to synthesize Aristotle’s conception of virtue with his own Christian worldview. So thorough was his admiration for the Greek that Aquinas called him “the philosopher.”

When Aquinas spoke of “sin” in  everyday life, he was usually thinking of Aristotle’s golden mean. For example, the “Summa Theologica” discusses the universal propensity to acquire knowledge that enables a good life. In Latin, Aquinas called it “studiositas.”

Studiositas helps us establish an ordered desire to learn. This virtue ensures that we seek knowledge for the right reasons, such as understanding the truth and cultivating wisdom. To Aquinas, this moderate approach to learning is ultimately in service of God, as worship of God ensures our moral development.

A lack of studiositas reveals a lack of interest in becoming a better person. This deficiency characterizes one extreme of studiositas, just like for Aristotle, cowardice describes the absence of courage. Aquinas didn’t discuss this lack in detail. He thought it was obvious that anyone who didn’t want to embark upon an ethical and spiritual journey would forego a good life.

Cover page of the "Summa Theologica," 1596 edition. Public Domain

The other extreme of studiositas is “curiositas,” which Aquinas described as a desire to know “which is in excess.” When studiositas is in excess, our yearning for knowledge is driven by wrong motives or pursued in harmful ways. In Aristotle’s terms, curiositas is a vice that distorts our pursuit of knowledge in the name of pride, vanity, power, and other detrimental intentions. Aquinas thought of it as a sin, for curiositas prevents us from living the life of faith that affords virtue and wellbeing.

On Grace

Aquinas agreed with Aristotle—attaining eudaimonia was partly beyond human control—but his explanation differed. The theologian maintained that we can never reach perfect eudaimonia in this life. Virtue on earth is possible and necessary, but it’s ultimately insufficient. Perfect eudaimonia consists in beatitude, a union with God that can only be fulfilled beyond the bounds of our mortality.

In addition to virtues, we need God to transform our nature so that we may participate in divine beatitude. Hence Aquinas’s amendment of Aristotle’s framework: “Virtue is a good quality of the mind, by which we live righteously, of which no one can make bad use, which God works in us, without us.”

Despite the criticisms some of his proposals received, Aquinas’s intellectual efforts helped build bridges between the classical world and Christianity. Fifty years after his passing, he was canonized by Pope John XXII. His genius also earned him a place in Dante’s “Divine Comedy,” where the saint’s deified soul dwells in the Heaven of the Sun alongside other sages.

As a theologian, Aquinas regularly engaged in abstract thinking. Yet he knew that the most important thing in life was to act by sound guidelines and beliefs. That’s why he thought deeply about moral integrity, so that future people could, too, live with virtue and good faith.

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