Thus when the will, which is an intermediate good, holds fast to the unchangeable good as something common rather than private – like the truth, which we have discussed at length without saying anything adequate – a person grasps the happy life. and the happy life, i.e. the attachment of the mind holding fast to the unchangeable good, is the proper and fundamental good for a human being. It also includes all the virtues, which no one can use for evil. although the virtues are great and fundamental goods in human beings, we thoroughly understand that they are proper to each person, not that they are common. Truth and wisdom, however, are common to all, and people become wise and happy by holding fast to them. of course, one person does not become happy by the happiness of another. even if you emulate another in order to be happy, you seek to become happy by means of what you saw made the other person happy, namely through the unchangeable and common truth. Nor does anyone become prudent by another person’s prudence, or is made courageous by another’s courage, or moderate by another’s moderateness, or just by another’s justice. Instead, you conform your mind to those unchangeable rules and beacons of the virtues, which live uncorruptibly in the truth itself and in the wisdom that is common, to which the person furnished with virtues whom you put forward as a model for your emulation has conformed and directed his mind.
Therefore, when the will adheres to the common and unchangeable good, it achieves the great and fundamental goods of a human being, despite being an intermediate good. But the will sins when it is turned away from the unchangeable and common good, towards its private good, or towards something external, or towards something lower. The will is turned to its private good when it wants to be in its own power; it is turned to something external when it is eager to know the personal affairs of other people, or anything that is not its business; it is turned to something lower when it takes delight in bodily pleasures. And thus someone who is made proud or curious or lascivious is captured by another life that, in comparison to the higher life, is death. (De libero arbitrio 2.19.52., trans. Peter King)