The four cardinal virtues are prudence, justice, fortitude, and temperance. They are called “cardinal”, from the Latin cardo, meaning “hinge”.

They represent, in other words, the pivotal virtues of the moral life. Prudence, however, is not only first in the order of priority, that is, usually listed first, but first in the order of primacy. No moral virtue is possible without prudence.

It is the defining quality that makes the brave individual brave, the just individual just, or the temperate individual temperate.

That said, something strikes a reader immediately, namely, that this is not the ordinary understanding of “prudence”. Being prudent usually means being cautious, careful, and risk-averse. The prudent individual takes little chances.

For the great thinkers of the Christian tradition, and others before them, however, prudence was synonymous with wisdom. Should we then change the word, to guarantee its real meaning? One may well be in favour of this.

In which case, “discernment” is perhaps a good alternative – though we should note with this term that we are in the moral realm, not the realm of the discernment of spirits. The traditional term, however, is hallowed from long usage, and I therefore retain it, only bearing in mind that in content and range it’s a great deal richer than we think.

The prudent individual is the individual who knows, for instance, whether courage means walking away or standing up to fight. Prudence determines the appropriate “form” of the virtue, what makes walking away the appropriate response in this situation.

It means that you cannot define in advance what form particular virtues take. You can say, as Aristotle did, that courage is the “mean” between rashness and cowardice. That gives you some idea of the parameters involved, but it yields no firm definition.

The reason is that virtue is always situated; circumstances condition its “form”. Kindness, for instance, may mean “tough love” in one set of circumstances, but warmth, even indulgence, in another.

Prudence is thus indispensable. It “tells” you what particular situations require. Aristotle spoke of it as the “eye” of the soul, and this notion of perception is key.

Prudence involves a way of seeing. Jesus also used the same metaphor: “If your eye is sound, your whole body (i.e., your entire self) will be filled with light. But if your eye is diseased, your whole body will be all darkness” (Mt 6: 23).

How then do we attain to soundness of sight? The metaphor implies, first, that we genuinely see things, that is, see them for what they are, that we are grounded in reality. Good intentions alone or meaning well are therefore not enough.

Seeing things for what they are is also not something to be simply assumed. The best of us edit reality all the time; we don’t see what we don’t want to see; we see things in a way that suits us; or we simply deny that things are what they are. All such subterfuges are foreign to prudence. Prudence implies perception grounded in truth.

It’s clear too that “seeing”, here is not just looking. It’s a mode of knowing. We imply this, when we say to ourselves, for instance, in moments of insight: “Ah, I now see…” What we refer to on such occasions is not actual sight. What we mean is we now understand.

Thomas Aquinas, the great medieval philosopher and theologian, lists several conditions for the development of prudence. The first thing he advises is the habit of contemplative reflection, and the reason for this is obvious. One has to become familiar with reality – with all that’s there. Perceiving and judging are to be rooted in what’s real.

Other qualities he notes are integrity in recollection, docility, and clear-sighted objectivity.

By “integrity in recollection” he meant storing our knowledge of reality without retouching, editing, or leaving things out. Memory is a sort of bank, into which we put happenings, occurrences, and events, to be drawn out or recalled on future occasions. Without integrity in our memory, we operate with a background of error and self-deception.

Second, docility. This is a literal translation of the Latin docilitas, and it means not docility, as in simple-mindedness, but as in the openness that recognises that life entails genuine variety in people, situations, and things. What it also implies is the ability to take advice, not from some vague sense of modesty, but from a real desire to understand.

A closed mind, or one that knows it all, is fundamentally a form of resistance to truth. It reveals an incapacity to honour the receptiveness necessary for genuine knowledge.

Thirdly, clear-sighted objectivity. This is the quality that allows you when confronted with a sudden event, not to close your eyes, and act blindly, hoping for the best. It is the clarity that helps you to see and decide swiftly, and in the best way, without vacillation or thoughtlessness.

Consider the situation of Solomon and the two mothers, and imagine the source of his ability to propose in that unforeseen circumstance that cutting the child in two was the fitting suggestion to make.

This sort of mental nimbleness presumes both spiritual and physical fitness. You can’t let your self go to seed generally and expect to see things clearly and decide well, especially when situations do not allow time for reflection.

Because prudence involves a translation from perceiving and judging to acting, it requires foresight, a capacity to estimate where things will lead, whether or not a particular action will lead to the desired end. This does not entail certainty.

It does not mean that in deciding we will be preserved from all anxiety. But there’s no waiting for complete freedom from anxiety. That way indecision lies; one never decides.

Prudence needs to be distinguished from its mirror opposite. The most characteristic form of this is cunning, the temperament that has regard only for “tactics”, which cannot face things squarely, or operate in a straightforward manner.

Crooked means can lead to good ends. Prudence, however, implies a concern for means appropriate to the matter at issue. This often means a silencing of the ego and its interests, so that reality itself can direct regarding the proper means for realising the particular end.

Aquinas traces failure in prudence to two sources, unchastity and covetousness, meaning on the one hand, a preoccupation with the sensual, and on the other, an immoderate straining after possessions. Both qualities are opposed to the fundamental bent of prudence, which is receptiveness to truth, trust, and unconcern for self-preservation, in a word, real humility.

To sum up, prudence is genuine perception; willingness to take advice; composure in the face of the unexpected; patience in deliberation; and boldness in action.

It entails straightforwardness, candour, simplicity of character, and superiority to “tactics”. In prudence the happiness of the active life is essentially comprised. Prudence means doing the truth.