The psychologist’s fallacy is a fallacy that occurs when an observer presupposes the objectivity of his own perspective when analyzing a behavioral event. The fallacy was named by William James in the 19th century. It is a specific form of the “similar to me” stereotype: what is unknown about another person is assumed, for simplicity, using things the observer knows about himself. Such a bias leads the observer to presuppose knowledge or skills, or lack of such, possessed by another person. For example, “I (or everyone I know or most people I know) don’t know very much about chemistry. Therefore I can assume that this other person knows very little about chemistry”. This assumption may be true in any number of specific cases, making inductive reasoning based on this assumption cogent, but is not applicable in the general case (there are many people who are very knowledgeable in the field of chemistry), and therefore deductive reasoning based on this assumption may be invalid.
The great snare of the psychologist is the confusion of his own standpoint with that of the mental fact about which he is making his report. I shall hereafter call this the ‘psychologist’s fallacy’ par excellence. (William James, Principles of Psychology volume I. chapter vii. p. 196, 1890)
Psychologist’s fallacy, the fallacy, to which the psychologist is peculiarly liable, of reading into the mind he is examining what is true of his own; especially of reading into lower minds what is true of higher. (James Mark Baldwin, Dictionary of Philosophy and Psychology volume II. p. 382/2, 1902)
A danger to be avoided known as the ‘psychologist’s fallacy’. This arises from the fact that the experimenter is apt to suppose that the subject will respond to a stimulus or an order in the same way as he himself would respond in the circumstances. (British Journal of Psychology. XXI. p. 243, 1931)