John McIntyre, at You Don't Say, has some cogent remarks on self-plagiarism:
Yesterday, writing at Poynter.org, Roy Peter Clark suggested that our current attitudes about plagiarism have conflated relatively minor or innocuous literary borrowings with serious thefts. One of the points he identified was the clamor about self-plagiarism. After quoting him, I'd like to add some observations.
Actually, he begins by quoting Judge Richard A. Posner's Little Book of Plagiarism: "Posner hits the target on this one: 'The temptation to lump distinct practices in with plagiarism should be resisted for the sake of clarity; "self-plagiarism," for example, should be recognized as a distinct practice and rarely an objectionable one.' All successful writers 're-purpose' their work for profit and influence, but they should always be forthright with potential publishers on whether the work is brand new or recycled."
I think of the practice of H.L. Mencken, who would write a short article for The Evening Sun, then revise and enlarge to magazine length, and finally repurpose it again for one of his books. (Bach and Handel regularly reworked material from one composition for another; were they self-plagiarists?)
In my opinion, there's are some even stranger things about this protean offense.
Here's one example. When a student buys an essay from an essay mill and submits it for a class assignment, that's a clearly culpable case of one variety of plagiarism. It doesn't really matter whether the essay was a basic pre-written model, or a more expensive custom-made product — though the latter is harder to detect and prove. In contrast, when a university president issues a statement ghostwritten by a staff member, or by someone hired for the occasion, that's the normal conduct of business. But if it turns out that the speechwriter copied some passages from material previously attributed to another source, that's plagiarism again.
This same weird ethos applies to ghostwritten articles and books. The fact that such a work was not written by its nominal author is not exactly a journalistic scoop, and indeed is probably not even a publishable observation by normal journalistic standards. Even if the ghostwriter hires a ghost-ghostwriter to do some of the work, that's about as exciting as an architect hiring a subcontractor. But suppose it turns out that the ghostwriter (or the ghost-ghostwriter) copied significant passages from material previously attributed to someone else, or written by an anonymous or collective author such as Wikipedia…
It's logical to want student work to represent the student's own capabilities (though not their capability to hire others to do their work for them). And it's logical not to care much whether executives or politicians write their own statements, speeches, and op-eds, though I think we should do a better job of explaining to students why the cases differ. But this leaves us (me, anyhow) uncertain how to evaluate the case of public intellectuals whose stuff is partly or entirely written by "researchers" or other "assistants".
And when those researchers or assistants or ghostwriters copy someone else's work? Well, um, …