As we explored in our last post, Saint Thomas Aquinas teaches that the virtue of prudence is not a simple inclination toward making good decisions, but rather a complex virtue composed of eight integral parts (or subvirtues). These are: memory, understanding, docility, shrewdness, reason, foresight, circumspection, and caution (cf. Summa Theologiae II-II, q. 49, a.1).
These integral parts are not optional enhancements; they are necessary elements that together constitute the fullness of prudence. Without them, prudence is incomplete and unreliable. Saint Thomas emphasizes this point by explaining that prudence is “right reason applied to action” (recta ratio agibilium, ST II-II, q.47, a.2), and right reasoning must begin from something—namely, from first principles. This is where the virtue of understanding comes in.
“Understanding denotes here, not the intellectual power, but the right estimate about some final principle, which is taken as self-evident… every process of reasoning must needs proceed from some understanding. Therefore since prudence is right reason applied to action, the whole process of prudence must needs have its source in understanding.”
— Summa Theologiae II-II, q.49, a.2
What Is the Virtue of Understanding?
The subvirtue of understanding (Latin: intellectus) provides the mind with an immediate grasp of first principles—those truths that are so foundational that they do not need to be proven, but rather serve as the starting points of practical reasoning. This is not the same as the intellectual virtue of understanding, which assists the intellect in grasping self-evident first principles of knowledge, such as “the whole is greater than the part” or “a thing cannot both be and not be at the same time,” nor is it the same as the Gift of the Holy Ghost known by the same name, which gives insight into divine truths established by God. The primary difference between understanding as an intellectual virtue and understanding as a subvirtue of prudence is that the former is primarily associated with universal truths and theoretical knowledge while the latter is associated with moral principles and serves as the foundation for right action.
Understanding as a part of prudence is deeply practical. It enables a person to grasp the proper end in a given moral situation. For example, in a family dispute, understanding helps us recognize that preserving peace and justice in the household is the foundational goal—before we even begin reasoning about how to achieve that peace.
“It belongs to understanding to apprehend intelligible truth… And since in every genus the principle is that which is first, it follows that understanding has to do with principles.”
— ST I, q.79, a.8
The Chair Analogy Revisited
To revisit our earlier analogy: think of prudence as a chair supported by eight legs—each leg being one of its integral parts. If understanding is missing, it is as if a crucial leg has broken off. The chair may look functional at first glance, but the moment we place any weight on it, it collapses. Likewise, prudence without understanding leads to shaky moral reasoning, where decisions may seem reasonable but are disconnected from the proper end or goal.
How Can We Grow in the Virtue of Understanding?
While understanding in this context is partly a natural aptitude—some are more intuitively able to see moral first principles—it can also be nurtured through habit, reflection, and moral formation. Here are some practical ways to grow in this foundational virtue:
- Meditation on First Principles
These principles form the bedrock of moral reasoning and help to orient our decisions rightly. Spend time each day reflecting on foundational moral truths such as:- “Bonum est faciendum et prosequendum, et malum vitandum.” (“Good is to be done and pursued, and evil is to be avoided.”) ST I-II, q.94, a.2
- “Human life is sacred.” Cf. Catechism of the Catholic Church (CCC) §2270
- “The end does not justify the means.” Cf. CCC1753
- “The common good must be pursued.” Cf. CCC1906–1909
- Frequent Examination of Conscience
This practice helps us build an intuitive awareness of moral priorities. By reviewing our day through the lens of key principles, we begin to notice where our instincts align—or fail to align—with them. - Study of Scripture and Moral Theology
Reading Sacred Scripture, the various Catechisms, the Church Fathers, or other moral theologians or sources such as the Handbook of Moral Theology by Father Dominicus Prümmer can deepen our understanding of the natural and divine law and first principles. Saint Thomas frequently quotes Scripture as the ultimate source of first principles.
- Mentorship and Spiritual Direction
Submitting our reasoning to a wise mentor or confessor helps refine our moral intuitions. We learn to “see what they see,” which over time forms our own capacity for right estimation. Aristotle famously taught that when we lack understanding in a particular area, we ought to seek out the counsel of one who is learned—someone whose knowledge has been tested and formed through experience and study. - Practice Silence and Contemplation
Saint Thomas was not only a theologian of remarkable intellect, but also a master of contemplation. He understood that truth is not merely discovered through reasoning. In the stillness of prayer, the soul becomes attuned to the divine, and the first principles of action—those foundational truths that guide the virtue of prudence—come into clearer focus. A story in tradition tells of a moment during the composition of the Summa Theologiae, when Saint Thomas found himself unable to resolve a particularly difficult theological point. Recognizing the limits of even the greatest human intellect, he turned not to more books, but to Our Lord in the Blessed Sacrament. Entering the chapel, he knelt near the Tabernacle and rested his head against It as though to physically incline his ear to the voice of Our Blessed Lord.
Conclusion: Understanding as the First Spark of Prudence
Without the subvirtue of understanding, the process of prudential judgment cannot even begin. It is the spark that lights the fire of moral reasoning. If we hope to become truly prudent people—able to make wise, timely, and virtuous decisions—we must begin by cultivating this first and most foundational of prudence’s integral parts.
In the next post, we will look at the virtue of docility, and how openness to instruction keeps our prudence both humble and dynamic.