I'm looking for a clear, definitive answer to the following question: Is taking someone else's writing, and changing some of the words, inherently plagiarism?
I find resources that describe plagiarism are usually a bit vague around this issue. For example, one commonly-quoted book says this (Pechenik, 2001, p. 10):
Don’t plagiarize. Express your own thoughts in your own words... Note, too, that simply changing a few words here and there, or changing the order of a few words in a sentence or paragraph, is still plagiarism. Plagiarism is one of the most serious crimes in academia.
Or this likewise from the IEEE Publications: Identifying Plagiarism page:
... we should be able to agree that changing only a few words or phrases or only rearranging the original sentence order of another author's work will be defined as plagiarism.
Now, the fact that these sources each refer to changing or moving "a few words" leaves open the question of whether changing or moving more words, or many words, would possibly be not-plagiarism. Is there any threshold at which changing words becomes not-plagiarism? Possibly all of them?
The practical concern I have is that recently I've gotten a high frequency of students I've caught for plagiarizing in my courses (around half) saying something like, "Ah yes, when I took that file I didn't change enough of the words because I was rushed for time. I'm sorry, next time I'll change more of the words."
Ultimately I'm wondering if the best response to that is, "That would still be plagiarism [even if you changed all of the words]!", or if the response needs to be something different and more complex. (I find that for such students with possible language problems, more complicated responses are likely to be disregarded, so I'm looking for a minimalist communication in these situations.)
The best answer will not go into discussions of practical issues of detecting plagiarism. A reference to some authoritative source on this issue would be a value-add.
It may be helpful to note that "plagiarism" is emphasized here because it's central to my institutions' (and others') academic integrity definitions and enforcement mechanisms. In our case, "Copying another person’s actual words or images..." is the primary (but not the only) example of what counts as plagiarism.