I'm not actively involved in academia at the moment so I don't know how much my opinion on this matter counts, but I've decided I don't like turnitin.com.

It seems to me that there is a finite amount of things that can be said on any given topic, and there is an even more finite (can there be degrees of finiteness?) amount of things that the typical undergrad would be inclined to say on any given topic. There is also a finite number of ways that any given idea can be expressed in a particular language.

If you have every student run every paper through turnitin.com, and you compare all papers to all previous papers, eventually there are going to be some matches that are pure coincidence. I'm sure I'm not the first person to think of using this particular thesis with these particular supporting points in my first essay for first-year English Lit, and someone else writing on the exact same topic might use one or two of the same turns of phrase as I do. The mroe papers are added to the database, the greater the chance of a coincidental match?

So what will happen to the first student who dilligently writes an essay in their own words, but it ends up getting flagged by turnitin.com. How will they convince the prof that they are being honest? Will their academic career be ruined?