Is it possible to appropriate the words or ideas of others without realizing it? Some authors, such as Robert Louis Stevenson, accused themselves of committing plagiarism (he came to believe he had appropriated much of “Treasure Island” from other authors). But some who have been accused of plagiarism, including Helen Keller, have pushed back strongly against such a charge, offering up unconscious appropriation as an excuse. Musicians have also been accused of this, and the famous case of ex-Beatle George Harrison is described in detail. Relying on a previous ruling known as the subconscious copying doctrine, the judge in Harrison’s case ruled that his copying had been done without conscious awareness but that he was still culpable. Experimental psychologists have been able to induce research participants into appropriating the responses of other participants without conscious awareness, suggesting that this phenomenon is real and not just a defense offered up by those accused of plagiarism. This can be explained as a failure of source monitoring, in which ideas that originated in the minds of others become confused with the products of one’s own cognitive processes.