The absence of good is a theologicaldoctrine that evil, unlike good, is insubstantial, so that thinking of it as an entity is misleading. Instead, evil is rather the absence or lack of good. It is typically attributed to St. Augustine of Hippo, who wrote: See also: "For evil has no positive nature; but the loss of good has received the name “evil.”" 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 appears only when sources of light are extinguished or obscured and ends when an object absorbs a disproportionate amount of the light that strikes it. This is illustrated by Lao Tzu in the Tao Te Ching quite well: The relationship between light and darkness is often used to frame a metaphorical understanding of good and evil. The 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, 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, 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. Then, goodness cannot be actively opposed, and power becomes a consequence of benevolence. However, evil is the default state of the universe, and good exists only through constanteffort; any lapse or redirection of good will apparently create evil out of nothing. This doctrine is also supported by the Baháʼí Faith. ʻAbdu'l-Bahá stated to a French Baháʼí woman:
