The nirvana fallacy is the informal fallacy of comparing actual things with unrealistic, idealized alternatives. It can also refer to the tendency to assume there is a perfect solution to a particular problem. A closely related concept is the "perfect solution fallacy".
By creating a false dichotomy that presents one option which is obviously advantageous—while at the same time being completely implausible—a person using the nirvana fallacy can attack any opposing idea because it is imperfect. Under this fallacy, the choice is not between real world solutions; it is, rather, a choice between one realistic achievable possibility and another unrealistic solution that could in some way be "better".
In La Bégueule (1772), Voltaire wrote Le mieux est l'ennemi du bien, which is often translated as "The perfect is the enemy of the good" (literally: "The better is the enemy of the good").
The nirvana fallacy was given its name by economist Harold Demsetz in 1969, who said:
The view that now pervades much public policy economics implicitly presents the relevant choice as between an ideal norm and an existing "imperfect" institutional arrangement. This nirvana approach differs considerably from a comparative institution approach in which the relevant choice is between alternative real institutional arrangements.
The perfect solution fallacy is a related informal fallacy that occurs when an argument assumes that a perfect solution exists or that a solution should be rejected because some part of the problem would still exist after it were implemented. This is an example of black and white thinking, in which a person fails to see the complex interplay between multiple component elements of a situation or problem, and, as a result, reduces complex problems to a pair of binary extremes.
It is common for arguments which commit this fallacy to omit any specifics about exactly how, or how badly, a proposed solution is claimed to fall short of acceptability, expressing the rejection only in vague terms. Alternatively, it may be combined with the fallacy of misleading vividness, when a specific example of a solution's failure is described in emotionally powerful detail but base rates are ignored (see availability heuristic).
The fallacy is a type of false dilemma.