In those cases I was alerted to plagiarism by the sudden appearance, in a paper that is otherwise a morass of grammatical errors, of a series of flawless sentences with complicated structures. The correct use of a semicolon is a big red flag for me. As is the use—and often misuse—of specialized jargon or technical language that I’ve not discussed with them in class. Then I type those sentences into Google, and they all wind up being smoking-gun cases of plagiarism. My favorite case this semester was plagiarism within plagiarism. When I informed this student that I suspected her paper was plagiarized, she said to me, “I got my paper from one of the students who was in your class last semester. How was I to know that she had plagiarized?” Which indicated to me, along with a number of the other email responses I got from students, that many of them don’t even know what plagiarism is.I'm also saddened by the instructor's observation that "the correct use of a semicolon" is an indicator that a college student might not have written it...
From an interview of a philosophy instructor in New York, posted at The New Inquiry, via The Dish.
Addendum: I liked this comment from reader .\\axxx re his experience with high-school science students:
"When the phrase "A white dwarf, also called a degenerate dwarf, is a small star composed mostly of electron-degenerate matter." occurred in multiple papers, and I pointed out that it was just a copy-paste from Wikipedia, one student got quite angry, saying they hadn't copy-pasted, they had printed it out then typed it in again!"