The Tree of the Virtues

How to use the tree

Start at the top. Each box on the trunk is a genus, and the label beside it is the difference that narrows it. The trunk follows the difference on the left; the difference on the right leads to a species that is set aside. Below the trunk, open any branch with the + button and select a virtue to see its definition, its place in the soul, the gift of the Holy Spirit that perfects it, the vices opposed to it, and where St. Thomas treats it in the Summa Theologiae.

The line style shows how a branch belongs to its parent: a solid line for a true species, a dashed line for an integral part, a dotted line for a potential part or annexed virtue, a fine dotted line for an act or effect, and a red dashed line for a counterfeit. Branches in italics are not virtues but the differences that divide them, taken from St. Thomas’s own reasons. The path at the top of the details panel works like a definition by genus and difference. Read it from the top down to see what a virtue is and what sets it apart.

Turn on Show vices in the tree to see the vices that flank each virtue, the vice of defect first and the vice of excess last, so that the virtue appears as the mean between them. Many virtues also have examples from the life of Christ, from Scripture, and from the saints.

What is a Porphyrian tree?

The Neoplatonist philosopher Porphyry (c. 234–c. 305) wrote the Isagoge, a short introduction to Aristotle’s Categories. Boethius translated it into Latin in the early sixth century, and for centuries it was the first logic book students read. Medieval teachers drew its method as a tree, the arbor porphyriana. It starts from a highest genus and divides it again and again by opposed differences until it reaches a lowest species. The classic tree runs: substance, body, living body, animal, rational animal, man.

St. Thomas Aquinas defines virtue in exactly this way. Its genus is quality, or more precisely habit; its difference is “good”; and an operative habit that is always ordered to good is a virtue (Summa Theologiae I-II q.55 a.4). Aquinas never drew this diagram himself. We have laid out his divisions, mostly from the Prima Secundae (questions 49–67) and the Secunda Secundae (questions 1–170), in the shape of a Porphyrian tree.

One caution: a strict Porphyrian tree contains only genera and species. Aquinas also speaks of integral and potential parts of a virtue, which are not species of it. The tree includes them because he does, and marks them with dashed and dotted lines.

How Aquinas divides the virtues

Virtues are told apart by their objects. If the object is God himself, as he exceeds the grasp of reason, the virtue is theological: faith, hope and charity. God alone infuses them, and we know of them only through revelation (I-II q.62 a.1–2; CCC 1812–1813).

The other virtues are human virtues (CCC 1804). The principles of human action are the intellect and the appetite, so every human virtue is either intellectual or moral (I-II q.58 a.3). The intellectual virtues are understanding, science and wisdom in the speculative intellect, and art and prudence in the practical intellect (I-II q.57). The moral virtues are told apart by their matter. Justice governs our actions toward others; temperance and fortitude govern the passions, restraining the ones that push us against reason and strengthening us against the ones that hold us back (I-II q.60–61).

The four cardinal virtues, from the Latin cardo, “hinge,” gather all the rest around them. Aquinas counts them in two ways that come out the same. Counted by their formal principle, the good of reason is either in reason itself (prudence), or put into our operations (justice), or into passions that need a curb (temperance) or a spur (fortitude). Counted by their subject, they perfect the reason, the will, the concupiscible appetite and the irascible appetite (I-II q.61 a.2; CCC 1805).

Integral, subjective and potential parts

In the Secunda Secundae, Aquinas organizes the moral life around the seven principal virtues. Each cardinal virtue has three kinds of parts (II-II q.48 a.1):

• Integral parts are like the wall, roof and foundation of a house: things that must come together for a complete act of the virtue. Memory, docility and foresight are integral parts of prudence.
• Subjective parts are like the ox and the lion under “animal”: the true species of the virtue. Chastity and sobriety are species of temperance.
• Potential parts are like the powers of the soul: related virtues that share something of the principal virtue’s way of acting, but in a lesser matter or without its full perfection. Religion, gratitude and truthfulness are annexed to justice; humility and meekness to temperance.

Aquinas also names counterfeits: vices or motives that imitate a virtue without being it. Prudence of the flesh, craftiness, guile and fraud are clever about means but serve the wrong end or use false means (II-II q.55). Someone may also act bravely out of ignorance, past success, training, passion, or a wish for honor or gain, without having fortitude at all (II-II q.123 a.1 ad 2).

Fortitude is a special case. Its matter, the danger of death, is too specific to be divided into species, so it has no subjective parts. Its four parts (magnanimity, magnificence, patience and perseverance) are integral when they concern danger of death and potential when they concern lesser hardships (II-II q.128).

Acquired and infused virtue

We acquire the human virtues by education, by deliberate acts, and by perseverance, and God’s grace purifies and elevates them (CCC 1804, 1810–1811). Aquinas teaches that with sanctifying grace and charity God also infuses moral virtues. They carry the same names as the acquired ones but differ in species, because they take their measure from God’s rule and not from human reason alone. His example: acquired temperance eats so as not to harm health or reason, while infused temperance also chastises the body for the sake of the kingdom (1 Corinthians 9:27; I-II q.63 a.3–4).

The virtues are also connected. No moral virtue is perfect without prudence, and prudence needs the moral virtues (I-II q.65 a.1). Charity is the “form” of all the virtues, directing their acts to God as our last end (II-II q.23 a.8). That is why St. Paul can say, “the greatest of these is love” (1 Corinthians 13:13).

Virtues, gifts and beatitudes

The seven gifts of the Holy Spirit make us docile to the Spirit’s promptings, as the moral virtues make the appetite docile to reason (I-II q.68 a.3–4; CCC 1830–1831). In the Secunda Secundae, Aquinas pairs each principal virtue with a gift and each gift with a beatitude:

Sources: II-II q.8 a.7; q.9 a.4; q.19 a.9 ad 1, a.12; q.45 a.6; q.52 a.4; q.121 a.2; q.139 a.2; q.141 a.1 ad 3. The gift of fear corresponds first to hope and secondarily to temperance.

Growing in virtue

The tree is not only a map for study. Each virtue sits between vices, often one by excess and one by defect, and each has a gift that perfects it. That makes the tree a good tool for an examination of conscience. Choose one virtue for a season, learn its parts, notice which opposed vice tempts you, and ask the Holy Spirit for the gift that goes with it. Virtues grow through repeated acts, through prayer, and above all through the sacraments, which pour out the grace that heals and raises our nature (CCC 1810–1811).

For more, see Aquinas 101, the Works of Mercy & the Virtues, and the full text of the Summa Theologiae at New Advent ↗.

The Thomistic Institute and the University of St. Thomas have built their own Porphyrian Tree of Virtue ↗, with pages on each virtue that draw on Scripture, the saints, literature and psychology. It is well worth exploring alongside this one.