A recently published article in The Scientist reminded me of a recent incident in my lab. One of my students handed me a draft of her latest manuscript, and as I was looking through the Methods section I noticed that the text was virtually identical to the text in the methods section of a paper that she had just published. Word for word. At this point I explained that this technically was plagiarism and possibly violation of copyright and that she should alter the text somewhat. "But why?" she said, "The methods themselves are the exact same ones I used in my previous paper and anyway, how can I plagiarize my own work?" She obviously has a good point. I know I've written about 28 different versions of my methods section and about as many versions of my opening paragraph. I mean, when you work in a given field you always cite the same references in your introduction and large chunks of your methods are identical. In how many ways can you describe the exact same experimental conditions? And yes, you could cite yourself, but it's nice to have a self-contained manuscript in which a reader does not have to look at your old papers in order to be able to understand it.
So why is it plagiarism? Because you are copying text of something that already has been published. And since most journals own the copyright to your manuscripts, re-using your own text verbatim is likely a copyright violation. It's a bit silly, but apparently that's the way it is and according to the article in The Scientist, papers have been retracted by journals because of this. My approach that I tell people in my lab is that it's OK to take the old methods and change them around a bit, but that the introduction should be written from scratch. They can read an old introduction and then replicate it by memory, and this is usually enough to make the two texts sufficiently different, but they should never cut and paste text form their old papers. Where I find a larger gray area is sharing text between grants and manuscripts. Is it OK to paste a particularly succinct and well-written paragraph from your latest manuscript into a new grant application? Likewise, could you lift a paragraph from a grant and put it in a manuscript? I would argue that the second is maybe OK, since the grant is not a published document, but that the first is somewhat more iffy. To be safe though, I usually just write things from scratch, and since I've written the same things so many times they always sounds similar... yet different.
What about you, readers, what is your view on self-plagiarism? Where do you draw the line in your own work?