Absence of good

Privatio Boni can be loosely translated as "privation of good." It is a theological doctrine that good and evil are, in some circumstances at least, asymmetrical. Strictly speaking, it holds that evil is insubstantial, so that thinking of it as an entity is misleading: it would be more constructive to speak only of it as the lack of good.

It is typically attributed to St. Augustine of Hippo, who wrote:

And in the universe, even that which is called evil, when it is regulated and put in its own place, only enhances our admiration of the good; for we enjoy and value the good more when we compare it with the evil. For the Almighty God, who, as even the heathen acknowledge, has supreme power over all things, being Himself supremely good, would never permit the existence of anything evil among His works, if He were not so omnipotent and good that He can bring good even out of evil. For what is that which we call evil but the absence of good? In the bodies of animals, disease and wounds mean nothing but the absence of health; for when a cure is effected, that does not mean that the evils which were present—namely, the diseases and wounds—go away from the body and dwell elsewhere: they altogether cease to exist; for the wound or disease is not a substance, but a defect in the fleshly substance,—the flesh itself being a substance, and therefore something good, of which those evils—that is, privations of the good which we call health—are accidents. Just in the same way, what are called vices in the soul are nothing but privations of natural good. And when they are cured, they are not transferred elsewhere: when they cease to exist in the healthy soul, they cannot exist anywhere else.

— St. Augustine of Hippo, Enchiridion of Augustine, Chapter 11: What is called Evil in the Universe is But the Absence of Good

Our perceptions are based on contrast, so that light and dark, good and evil, are imperceptible without each other; in this context, these sets of opposites show a certain symmetry. But a basic study of optics teaches us that light has a physical presence of its own, whereas darkness does not: no "anti-lamp" or "flashdark" can be constructed which casts a beam of darkness onto a surface that is otherwise well-lit. Instead, darkness only appears when sources of light are extinguished or obscured, and only persists when an object absorbs a disproportionate amount of the light that strikes it.

The relationship between light and darkness is often used to frame a metaphorical understanding of good and evil. This metaphor can be used to answer the problem of evil: If evil, like darkness, does not truly exist, but is only a name we give to our perception of privatio boni, then our widespread observation of evil does not preclude the possibility of a benevolent, omniscient, and omnipresent God.

If the metaphor can be extended, and good and evil share the same asymmetry as light and darkness, then evil can have no source, cannot be projected, and, of itself, can offer no resistance to any source of good, no matter how weak or distant. In this case, goodness cannot be actively opposed, and power becomes a consequence of benevolence. However, in this case evil is the default state of the universe, and good exists only through constant effort; any lapse or redirection of good will apparently create evil out of nothing.