By altering some words and deleting others, my student hoped to obscure the stolen material. This trick might have worked -- if I didn't have Google to track down phrases. Even with Google as an anti-plagiarist tool, the student might have gotten away with the plagiarism by altering more words.In fact one of the things that made me realize the value of editorial fatigue as a possible way of telling the direction of dependence was seeing it in student essays. I remember a student in one of the first classes I taught in Birmingham in 1995 copying a paragraph from Sanders and Davies's Studying the Synoptic Gospels in which reference was being made to something Sanders and Davies had previously discussed but the student had not.
Inevitably, though, Goodacre's principle proves its value, for somewhere in the paper of even a clever plagiarist, editorial fatigue sets in, and the plagiarist slips, allowing a telling phrase from the original to remain. In this particular case, the phrase, as noted above, was: "could not lead to large scale duplication."
Jeffery's discussion about plagiarism is useful and interesting, and draws attention ot the value of Google as a tool to catch student plagiarists. I have used it the same way myself and have frequently been able to convict students on the basis of searches done via Google. I remain concerned about several things, though, in the student plagiarist culture:
(1) It's easier to catch the weak plagiarists who betray their sources all too quickly because they do not think to hide or know how to hide the distinctive phrases of their sources. But how easy is it to catch the better plagiarists, who can see the distinctive, Google-friendly phrases in their source material, and who change words but not sentence structure?
(2) On-line plagiarism is so easy to do that, as Jeffery points out, it is relatively easy to catch. But does this mean that some of our students are getting away with book-plagiarism all the more easily? If someone plagiarizes Sanders, Crossan or Wright, you can bet that we'll be able to find it. But if they plagiarize Howard Clark Kee, are we going to spot it?
(3) Does our satisfaction in discovering the on-line plagiarists mask us from seeing the students who have paid someone $75 to write their essay for them, or who have pulled their essay from a model stock essay for which they have paid $25 access? Google is not going to spot those, and however much we might suspect, are we going to be able to convict?
One of the things that this convinces me of is the importance of maintaining examinations as a key element in undergraduate assessment, however much students might prefer the take-home essay. In my courses at Duke, I have a variety of assessment methods in the same course, but with at least 50% going in as examination, one of the advantages of which is the confirmation that this element cannot have been plagiarized.
Addendum: I was once faced with a situation in which we had two very similar essays, but one was inferior to the other. A colleague argued that he thought the worse essay had been copied from the better essay. I found myself arguing that both had been copying from a hypothetical lost source, to the amusement of several other colleagues present at the examiners' meeting. A means of resolving the situation was suggested: we get both students in and interview them separately. And it turned out that I was wrong: there was no hypothetical third source. One student confessed to having copied from the other, and the other student admitted to having lent their work to the other, and was very annoyed that the other student had copied their work. The moral of the story: is it (a) Don't hypothesize unnecessary documents or (b) it'd be great if we could interview Matthew and Luke?
Update (Monday, 21.18): Jeffery has a great follow-up, Netting Plagiarists.