(a) Understanding or intelligence is the habit of perceiving truths that are not in need of proof, as being self-evident. Axiomatic truths or first principles are the object of this virtue. (b) Knowledge or science is the habit of perceiving truths that are learned from other truths by argumentation, and that are ultimate in some category of being. The object of this virtue embraces the various sciences (like astronomy) which are conclusions from principles. (c) Wisdom is the habit of learning through reasoning the truth that is absolutely ultimate; it is the knowledge of things in their supreme cause, God. Examples are theology and philosophy in their highest sense. 146. The practical intellectual virtues are two: prudence and art. (a) Prudence is an intellectual virtue which indicates in individual cases what is to be done or what is to be omitted, in order that one may act according to the requirements of good morals. (b) Art is an intellectual virtue which indicates in individual cases how one must act in order to produce things that are useful or beautiful (e.g., music, painting, building, etc.). 147. The intellectual virtues, except prudence, are not perfect virtues, since, While they make an act good, they do not necessarily make the agent good. A man may have great knowledge about morality, or be able to produce excellent works of art, and at the same time be not virtuous, or have no love for his work. 148. Prudence is an intellectual virtue, since it resides in the intellect; but it is also classed among the moral virtues, since its object is the direction of human acts to their right end. 149. The moral virtues are those habits that perfect the will and the sensitive appetite with reference to their immediate and respective objects; that is, they are habits concerned with acts as means to the Last End. They make the act good, and make good also him who performs it; and they are thus superior as virtues to the intellectual habits. 150. There are four principal moral virtues: (a) in the intellect there is prudence, which guides all the actions and passions by directing the other moral virtues to what is good according to reason; (b) in the will there is justice, which inclines a person to make his actions accord with what he owes to others; (c) in the irascible appetite is fortitude, which subjects to reason the passions that might withdraw from good, such as fear of dangers and labors; (d) in the concupiscible appetite is temperance, which represses the motions of passions that would impel one to some sensible good opposed to reason. These four virtues are also called cardinal virtues, because all the other moral virtues hinge on them.