The “stolen concept” fallacy, first identified by Ayn Rand, is the fallacy of using a concept while denying the validity of its genetic roots, i.e., of an earlier concept(s) on which it logically depends.

“Philosophical Detection”
Philosophy: Who Needs It, 22

As they feed on stolen wealth in body, so they feed on stolen concepts in mind, and proclaim that honesty consists of refusing to know that one is stealing. As they use effects while denying causes, so they use our concepts while denying the roots and the existence of the concepts they are using.

“Galt’s Speech”
For the New Intellectual, 154

When modern philosophers declare that axioms are a matter of arbitrary choice, and proceed to choose complex, derivative concepts as the alleged axioms of their alleged reasoning, one can observe that their statements imply and depend on “existence,” “consciousness,” “identity,” which they profess to negate, but which are smuggled into their arguments in the form of unacknowledged, “stolen” concepts.

They proclaim that there are no entities, that nothing exists but motion, and blank out the fact that motion presupposes the thing which moves, that without the concept of entity, there can be no such concept as “motion.”

. . . They proclaim that there is no law of identity, that nothing exists but change, and blank out the fact that change presupposes the concepts of what changes, from what and to what, that without the law of identity no such concept as “change” is possible.

. . . “You cannot prove that you exist or that you’re conscious,” they chatter, blanking out the fact that proof presupposes existence, consciousness and a complex chain of knowledge: the existence of something to know, of a consciousness able to know it, and of a knowledge that has learned to distinguish between such concepts as the proved and the unproved.

“Galt’s Speech”
For the New Intellectual, 154

The arguments of those who attack the senses are merely variants of the fallacy of the “stolen concept.”

“Foreword to the First Edition”
Introduction to Objectivist Epistemology, 3

Observe that Descartes starts his system by using “error” and its synonyms or derivatives as “stolen concepts.”

Men have been wrong, and therefore, he implies, they can never know what is right. But if they cannot, how did they ever discover that they were wrong? How can one form such concepts as “mistake” or “error” while wholly ignorant of what is correct? “Error” signifies a departure from truth; the concept of “error” logically presupposes that one has already grasped some truth. If truth were unknowable, as Descartes implies, the idea of a departure from it would be meaningless.

The same point applies to concepts denoting specific forms of error. If we cannot ever be certain that an argument is logically valid, if validity is unknowable, then the concept of “invalid” reasoning is impossible to reach or apply. If we cannot ever know that a man is sane, then the concept of “insanity” is impossible to form or define. If we cannot recognize the state of being awake, then we cannot recognize or conceptualize a state of not being awake (such as dreaming). If man cannot grasp X, then “non-X” stands for nothing.

“Leonard Peikoff, ‘Maybe You’re Wrong’”
The Objectivist Forum, April 1981, 9

Particularly since Kant, the philosophical technique of concept stealing, of attempting to negate reason by means of reason, has become a general bromide, a gimmick worn transparently thin.

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