Recently two popular historians were discovered to have lifted passages from other historians' books. They identified the sources in footnotes, but they failed to place quotation marks around the purloined passages. Both historians were quickly buried under an avalanche of criticism. The scandal will soon be forgotten, but it leaves in its wake the questions What is "plagiarism"? and Why is it reprobated? These are important questions. The label "plagiarist" can ruin a writer, destroy a scholarly career, blast a politician's chances for election, and cause the expulsion of a student from a college or university. New computer search programs, though they may in the long run deter plagiarism, will in the short run lead to the discovery of more cases of it.
We must distinguish in the first place between a plagiarist and a copyright infringer. They are both copycats, but the latter is trying to appropriate revenues generated by property that belongs to someone else—namely, the holder of the copyright on the work that the infringer has copied. A pirated edition of a current best seller is a good example of copyright infringement. There is no copyright infringement, however, if the "stolen" intellectual property is in the public domain (in which case it is not property at all), or if the purpose is not appropriation of the copyright holder's revenue. The doctrine of "fair use" permits brief passages from a book to be quoted in a book review or a critical essay; and the parodist of a copyrighted work is permitted to copy as much of that work as is necessary to enable readers to recognize the new work as a parody. A writer may, for that matter, quote a passage from another writer just to liven up the narrative; but to do so without quotation marks—to pass off another writer's writing as one's own—is more like fraud than like fair use.