Absence of good
The absence of good (), also known as the privation theory of evil, is a theological and philosophical doctrine that evil, unlike good, is insubstantial, so that thinking of it as an entity is misleading. Instead, evil is rather the absence, or lack ("privation"), of good. This also means that everything that exists is good, insofar as it exists; and is also sometimes stated as that evil ought to be regarded as nothing, or as something non-existent. It is often associated with a version of the problem of evil: if some things in the world were to be admitted to be evil, this could be taken to reflect badly on the creator of the world, who would then be difficult to admit to be completely good. The merit of the doctrine in serving as a response to this version of the problem of evil is disputed. History

Ancient Greek and Hellenistic philosophy 
The doctrine is sometimes said to be rooted in Plato. While Plato never directly stated the doctrine, it was developed, based on his remarks on evil, by the Neoplatonist philosopher Plotinus, chiefly in the eighth tractate of his First Ennead. The following quotation from that tractate, in which evil is described as non-being, illustrates this:As these are real beings, and as the first Principle is their superior, evil could not exist in such beings, and still less in Him, who is superior to them; for all these things are good. Evil then must be located in non-being, and must, so to speak, be its form, referring to the things that mingle with it, or have some community with it. This "non-being," however, is not absolute non-being. Its difference from being resembles the difference between being and movement or rest; but only as its image, or something still more distant from reality. Within this non-being are comprised all sense-objects, and all their passive modifications; or, evil may be something still more inferior, like their accident or principle, or one of the things that contribute to its constitution. To gain some conception of evil it may be represented by the contrast between measure and incommensurability; between indetermination and its goal; between lack of form and the creating principle of form; between lack and self-sufficiency; as the perpetual unlimited and changeableness; as passivity, insatiableness, and absolute poverty. Those are not the mere accidents of evil, but its very essence; all of that can be discovered when any part of evil is examined. The other objects, when they participate in the evil and resemble it, become evil without however being absolute Evil. Ancient and medieval Christian thought 
Neoplatonism was influential on St. Augustine of Hippo, with whom the doctrine is most associated. Augustine gave an argument for the theory in chapter 12 (paragraph 18) of book 7 of his Confessions:And it was made clear unto me that those things are good which yet are corrupted, which, neither were they supremely good, nor unless they were good, could be corrupted; because if supremely good, they were incorruptible, and if not good at all, there was nothing in them to be corrupted. For corruption harms, but, less it could diminish goodness, it could not harm. Either, then, corruption harms not, which cannot be; or, what is most certain, all which is corrupted is deprived of good. But if they be deprived of all good, they will cease to be. For if they be, and cannot be at all corrupted, they will become better, because they shall remain incorruptibly. And what more monstrous than to assert that those things which have lost all their goodness are made better? Therefore, if they shall be deprived of all good, they shall no longer be. So long, therefore, as they are, they are good; therefore whatsoever is, is good. That evil, then, which I sought whence it was, is not any substance; for were it a substance, it would be good. For either it would be an incorruptible substance, and so a chief good, or a corruptible substance, which unless it were good it could not be corrupted. I perceived, therefore, and it was made clear to me, that Thou made all things good, nor is there any substance at all that was not made by You; and because all that You have made are not equal, therefore all things are; because individually they are good, and altogether very good, because our God made all things very good.In his Enchiridion, Augustine explained the doctrine differently, by analyzing different examples of evils:

Augustine also mentioned the doctrine in passing in his City of God, where he wrote that "evil has no positive nature; but the loss of good has received the name 'evil.'" Through the influence of Augustine, this doctrine influenced much of Catholic thought on the subject of evil. For instance, Boethius famously proved, in Book III of his Consolation of Philosophy, that "evil is nothing". The theologian Pseudo-Dionysius the Areopagite also states that all being is good, in Chapter 4 of his work The Divine Names. Further to the East, John of Damascus wrote in his Exact Exposition of the Orthodox Faith (book 2, chapter 4) that "evil is nothing else than absence of goodness, just as darkness also is absence of light. For goodness is the light of the mind, and, similarly, evil is the darkness of the mind." Thomas Aquinas concluded, in article 1 of question 5 of the First Part of his Summa Theologiae, that "goodness and being are really the same, and differ only in idea". Early modern philosophy and poetry 
The philosopher Baruch Spinoza also agreed with the doctrine, when he said: "By reality and perfection I mean the same thing" (Ethics, part II, definition VI). He clarified this definition in the preface to part IV of the same work:Perfection and imperfection, then, are in reality merely modes of thinking, or notions which we form from a comparison among one another of individuals of the same species; hence I said above (II. Def. vi. ), that by reality and perfection I mean the same thing. For we are wont to refer all the individual things in nature to one genus, which is called the highest genus, namely, to the category of Being, whereto absolutely all individuals in nature belong. Thus, in so far as we refer the individuals in nature to this category, and comparing them one with another, find that some possess more of being or reality than others, we, to this extent, say that some are more perfect than others. [...]

As for the terms good and bad, they indicate no positive quality in things regarded in themselves, but are merely modes of thinking, or notions which we form from the comparison of things one with another. Thus one and the same thing can be at the same time good, bad, and indifferent. For instance, music is good for him that is melancholy, bad for him that mourns; for him that is deaf, it is neither good nor bad. Nevertheless, though this be so, the terms should still be retained. For, inasmuch as we desire to form an idea of man as a type of human nature which we may hold in view, it will be useful for us to retain the terms in question, in the sense I have indicated.Leibniz adhered to the doctrine as well, and employed it as part of his theodical argument that the actual world is the best of all possible worlds. John Milton, according to C.S. Lewis's preface to Paradise Lost, also believed in the theory; John Leonard's introduction to the same poem also uses the theory to interpret one of its passages. Both Lewis and Leonard cite Augustine as a source on the theory. Late modern religion 
The doctrine is also held by the Baháʼí Faith. ʻAbdu'l-Bahá stated to a French Baháʼí woman:

Criticism as a theory of evil

Various philosophers have proposed that the privation theory of evil is inadequate in some respect, so that non-privative evils must be admitted in at least some cases. A typical example is Bertrand Russell, who criticized the doctrine in his essay The Elements of Ethics:

Sorrow 
Pain and sorrow, mentioned by Russell in the quote above, are popular alleged counterexamples. The Stanford Encyclopedia of Philosophy article on "The Concept of Evil", written by philosopher Todd Calder, also says that "it seems that we cannot equate the evil of pain with the privation of pleasure or some other feeling. Pain is a distinct phenomenological experience which is positively bad and not merely not good." Thomas Aquinas, a proponent of the privation theory, argued against this opinion in his Summa Theologiae:[...] supposing the presence of something saddening or painful, it is a sign of goodness if a man is in sorrow or pain on account of this present evil. For if he were not to be in sorrow or pain, this could only be either because he feels it not, or because he does not reckon it as something unbecoming, both of which are manifest evils. Consequently it is a condition of goodness, that, supposing an evil to be present, sorrow or pain should ensue. Cruelty 
P.M.S. Hacker, in his book The Moral Powers, repeated the alleged example of cruelty, also mentioned by Russell: "The idea that evil is privative, that is, it consists in the absence of good, stripped of its theological trappings, is unconvincing. There is nothing privative about taking pleasure in the agony of others, or feeling joy at the sight of their torment." Opposition between appearances 
Immanuel Kant believed that, while the doctrine is true of concepts of the understanding, it is nevertheless false about the world as it appears to the senses. In a remark to the section of the Critique of Pure Reason entitled the "Amphiboly of the Conceptions of Reflection", he criticized the Leibnizian school of philosophy for not acknowledging this possibility of merely phenomenal opposition:The principle: "Realities (as simple affirmations) never logically contradict each other," is a proposition perfectly true respecting the relation of conceptions, but, whether as regards nature, or things in themselves (of which we have not the slightest conception), is without any the least meaning. For real opposition, in which A − B is = 0, exists everywhere, an opposition, that is, in which one reality united with another in the same subject annihilates the effects of the other—a fact which is constantly brought before our eyes by the different antagonistic actions and operations in nature, which, nevertheless, as depending on real forces, must be called realitates phaenomena. General mechanics can even present us with the empirical condition of this opposition in an à priori rule, as it directs its attention to the opposition in the direction of forces—a condition of which the transcendental conception of reality can tell us nothing. Although M. Leibnitz did not announce this proposition with precisely the pomp of a new principle, he yet employed it for the establishment of new propositions, and his followers introduced it into their Leibnitzio-Wolfian system of philosophy. According to this principle, for example, all evils are but consequences of the limited nature of created beings, that is, negations, because these are the only opposite of reality. (In the mere conception of a thing in general this is really the case, but not in things as phenomena.) In like manner, the upholders of this system deem it not only possible, but natural also, to connect and unite all reality in one being, because they acknowledge no other sort of opposition than that of contradiction (by which the conception itself of a thing is annihilated), and find themselves unable to conceive an opposition of reciprocal destruction, so to speak, in which one real cause destroys the effect of another, and the conditions of whose representation we meet with only in sensibility. Criticism as theodicy 
Some criticisms focus on the merit of the privation theory of evil as a response to the so-called problem of evil. For instance, P.M.S. Hacker states:Even if evil is privative like darkness, it is unclear why that relieves God of the responsibility of allowing it – after all, he could presumably have created a universe of light or not have created the universe at all.Todd Calder concurs:One problem with the privation theory's solution to the problem of evil is that it provides only a partial solution to the problem of evil since even if God creates no evil we must still explain why God allows privation evils to exist (See Calder 2007a; Kane 1980). References

Good and evil
Metaphysics of religion
Systematic theology
Bahá'í belief and doctrine