Mark Twain accused himself of it. So did Rod Stewart, Robert Louis Stevenson, and George Harrison.

When confronted with evidence of a strong resemblance between their own work and the creations of others, they defended themselves in the same way, claiming to have appropriated unwittingly and “unconsciously.”

But is unconscious plagiarism a real phenomenon, or is it simply an excuse for carelessness, or even outright theft?

In conducting research for my new book, Strikingly Similar: Plagiarism and Appropriation from Chaucer to Chatbots, I examined over four thousand claims of appropriation, infringement, and plagiarism. I was struck by how often authors, songwriters, and other artists expressed astonishment when these similarities were pointed out to them.

In Twain’s case, the issue was the similarity between the dedication for his Innocents Abroad (1869) and the inscription in Oliver Wendell Holmes’s Songs in Many Keys (1862)—a book that Twain knew well. A friend pointed out the resemblance, and Twain would later publicly out himself at a dinner held in Holmes’s honor.

A decade after penning Treasure Island (1883), Robert Louis Stevenson noted—with a fair degree of dismay—a striking similarity between elements of his book and details mentioned in Washington Irving’s Tales of a Traveler (1824).

In Rod Stewart’s case, it was the strong resemblance between his “Da Ya Think I’m Sexy” (1978) and the Brazilian artist Jorge Ben Jor’s song “Taj Mahal” (1977). In his autobiography, Stewart speculated that he had heard “Taj Mahal” during the Carnaval do Rio de Janeiro, when Ben Jor’s song was getting massive airplay.

Most famously, Harrison released “My Sweet Lord” in 1978 but was taken to task for appropriating the Chiffons’ “He’s So Fine,” which dropped in 1963. The song was a massive hit for the girl group, and as a fellow musician, Harrison undoubtedly heard it many times.

If we take these artists at their word, and accept that their copying was unintentional, is there any evidence that appropriation can occur without conscious awareness?

Creating Plagiarism in the Lab

Psychologists refer to the phenomenon as cryptomnesia—a memory glitch that most of us have experienced. Perhaps you’ve told a friend a humorous story, only to have your friend indignantly reply that they had told you that story previously.

Can this sort of phenomenon be studied experimentally? In research conducted by Alan Brown and Dana Murphy, participants played a game in which they took turns coming up with examples of categories, such as “articles of clothing” and “musical instruments.” The participants worked in small groups, generating words like “jacket” or “guitar,” but were warned not to offer up any term previously mentioned by other players (Brown & Murphy, 1989).

After several rounds of the game, the participants were asked to recall the words that they themselves had generated and were also asked to generate four new items that no one else had mentioned. Even when asked if they were “positive” that the items they listed were new, between 30% and 50% of these terms had, in fact, been proffered by another participant.

In a later study, subjects played a similar game and had to think of novel uses for familiar objects (such as “a watering can” for “shoe”). They returned three months later and were asked to recall the uses they had generated earlier, as well as new uses that no one had mentioned previously. The researchers found that rates of unconscious plagiarism increased after this delay (Stark & Perfect, 2007). So at least in these limited experimental contexts, the phenomenon has been shown to have some basis in reality.

Fear of Unconscious Plagiarism

Writers and musicians themselves are all too aware of this possibility. For example, Margit Sandemo, the Scandinavian author who wrote dozens of novels, told an interviewer that she read much less as she got older, lest she unconsciously appropriate story ideas or other elements from another writer.

Thomas Shapcott, an Australian writer, originally wanted to be a composer. But as a teen, he discovered he had unconsciously plagiarized a composition by Ernst Bloch for his own string quartet. This dispiriting realization led him to abandon composition and to become a tax accountant, although he later achieved artistic prominence as a poet and a novelist.

Forgiven . . . or Fined?

The consequences for unconscious plagiarism vary significantly, as we see if we return to the four men mentioned earlier. Twain was forgiven by Holmes, who magnanimously wrote that “we all unconsciously work over ideas gathered in reading and hearing, imagining they were original with ourselves” (Twain, 1910). Robert Louis Stevenson made his confession a few months before his death in 1894, and this admission did nothing to blunt the popularity of his coming-of age novel.

The consequences for the two musicians, however, were rather different.

Ben Jor initiated an infringement suit against Stewart, but the case was settled when Stewart agreed to donate his royalties from “Da Ya Think I’m Sexy” to UNICEF.

Harrison was involved in lengthy litigation initiated by the rights holder for “He’s So Fine.” Five years after the suit was filed, Harrison finally had his day in court and had to admit he was familiar with the Chiffons’ best-selling recording. The judge in the case ruled against him, stating that “This is, under the law, infringement of copyright, and is no less so even though subconsciously accomplished” (Bright Tunes Music Corp. v. Harrisongs Music, 1976).

The former Beatle was initially ordered to pay over $2 million in damages, but this was later reduced to $587,000 in 1981 (over $2 million today). The case wasn’t finally settled until 1998, and just three years before Harrison’s death at age 58.

In short, unintentional and unconscious plagiarism does seem to be a real phenomenon, but as Harrison and others have discovered, it is a defense that offers no legal protection—and the consequences can be costly.

Bright Tunes Music Corp. v. Harrisongs Music, Ltd., 420 F. Supp. 177 (S.D.N.Y. 1976).

Brown, A. S., & Murphy, D. R. (1989). Cryptomnesia: Delineating inadvertent plagiarism. Journal of Experimental Psychology: Learning, Memory, and Cognition, 15(3), 432–442.

Clemens, S. L. (1910). Mark Twain’s speeches. Harper & Brothers.

Stark, L., & Perfect, T. J. (2007). Whose idea was that? Source monitoring for idea ownership following elaboration. Memory, 15(7), 776–783.

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