Frozen Abstraction

The frozen abstraction is the error of substituting one particular concrete for the wider abstraction that subsumes it — treating a single instance of a category as though it were the whole category, so that the alternatives within it disappear from view. The term is Ayn Rand's, introduced in her essay "Collectivized Ethics".

“The fallacy of the "frozen abstraction" consists of substituting some one particular concrete for the wider abstract class to which it belongs.”
~ Ayn Rand, "Collectivized Ethics", The Virtue of Selfishness

The paradigm case

Rand's own example is the substitution of altruism for morality.

Morality is the wider class: the whole subject of what a code of values should be and why. Altruism is one answer within it. Freeze the abstraction, and "morality" comes to mean altruism, with the result that:

Every ethical dispute becomes a dispute over which version of altruism to adopt — service to God, to society, to the state, to the race — rather than over whether the premise is true.
A person who rejects altruism is heard as rejecting morality itself, and is asked to defend amoralism rather than the position he actually holds. See Egoism.
The one question that matters — for whose benefit should a man act, and why — is never reached, because the frozen abstraction has already answered it silently.

The damage is not that a false conclusion is asserted. It is that the alternative was removed from the concept before anyone got to argue.

Other instances

"Government" frozen to one form of it. Treating the choice as between the state as currently constituted and no state at all, so that a differently limited government is not a candidate. See Government and Anarchism.
"Selfishness" frozen to the brute. Taking one caricature of self-interest as the whole concept, which is what makes the package deal around the word effective.
"Capitalism" frozen to the mixed economy. Treating the existing system as what the concept names, so that objections to today's arrangements are heard as objections to a free market. See Capitalism.
"Rights" frozen to one enumerated list. Treating a particular legal codification as exhausting the concept rather than as one attempt to apply it. See Rights.

Why it is hard to notice

A frozen abstraction produces no visible gap. The word is still in use, still applied to real cases, and the person using it can supply an example on request — the concrete it was frozen to. What is missing is the rest of the class, and nothing in ordinary use draws attention to an absence.

It is also self-sustaining. Once "morality" means altruism, the vocabulary needed to state the alternative has been absorbed: there is no neutral term left in which to raise the question. This is the same mechanism by which a package deal forecloses a debate, run in the opposite direction — narrowing a concept rather than widening it past its referents.

The corrective is to name the genus explicitly. Ask what wider class the term belongs to, what else falls under that class, and what distinguishes the instance in front of you from the others. See Definitions, Rule of Fundamentality and Hierarchy.

Common misunderstandings

That it is the same as a hasty generalisation. A hasty generalisation draws too wide a conclusion from too few cases. A frozen abstraction has the scope of the concept itself wrong, before any generalising begins.
That using a typical example commits it. Illustrating an abstraction with a representative case is ordinary and necessary. The error is treating that case as the abstraction's entire content.
That it only affects philosophy. It is at its most effective in political argument, where terms like democracy, freedom and capitalism are routinely frozen to whichever instance the speaker has in mind.
That naming it wins the argument. It reopens one. What the wider class actually contains, and which member is correct, still has to be established.

Discussion

References

Rand, Ayn. "Collectivized Ethics", The Virtue of Selfishness. New American Library, 1964.
Rand, Ayn. Introduction to Objectivist Epistemology. 2nd edition, Meridian, 1990.
Peikoff, Leonard. Objectivism: The Philosophy of Ayn Rand, chapter 3.