The courts can be as fuzzy about what constitutes fair use as they are about what constitutes substantial similarity. In practice, the courts find infringement only in instances where language, images, or music were lifted wholesale. They rarely consider cases in which a character was copied or a plot was stolen. Thousands of writers bring suit each year claiming their copyright has been violated, but almost none win satisfaction in court. Book and software pirates are prosecuted under the copyright laws, but pirates are not really plagiarists.
Reprimands can come from the associations or from colleges and universities themselves.
Accusations of plagiarism seem to be the greatest deterrent. Some say accusations of plagiarism fly too freely. In a celebrated case, Abraham Lincoln biographer Stephen Oates was said to have ripped off a widely read 1952 Lincoln biography by Benjamin Thomas. In 1991, the American Historical Association criticized Oates for not adequately footnoting his use of Thomas' book. No legal charges were brought.