One of Douglas Hofstadter's more interesting (and convincing) articles in his monthly column for Scientific American in the 1980s, "Metamagical Themas" (reprinted in a book of the same name), was on how creativity comes from variations on a theme. Most truly creative work comes from extending existing ideas.
Plagiarism is a matter of degree. Handel could get away with stealing a Bononcini tune and saying "It was too good for him -- he didn't know what to do with it". Others borrowed with acknowledgement, writing "Variations on a theme by Paganini", "Suite on themes from Carmen", and so on.
In the jazz world, a "composition" by, say, Gershwin is little more than a basic tune and chord progression, followed by variations on the same progression. Nonetheless, Gershwin is carefully credited and royalties are paid. In the bebop era, musicians like Charlie Parker took the chord changes of standards (especially "I got rhythm"), made some substitutions, played frenzied tunes on top, and claimed copyright for the resulting compositions (many of which remain standards today). Fair enough -- you have to strain to hear "What is this thing called love?" in Gillespie's "Hot house".
On the other hand, on a recent Kenny Barron CD I picked up (Live at Bradley's II: The Perfect Set), "The Only One" is attributed to Barron but, the liner notes say, is "based on" Thelonious Monk's "Hackensack". To my ears, at least, it isn't "based on" Hackensack: it is Hackensack. (The CD contains two other Monk tunes, properly attributed.) Barron's "based on Monk" caveat would have been perfectly adequate if it had been "based on Paganini", but with Monk it means the difference between paying royalties and not paying royalties.
But is it so bad? The "statement" of Hackensack -- as in any jazz cover -- is very brief, only one chorus at the beginning. Jazz solos are full of quotes from other tunes (Paul Desmond told entire stories in quotes) and aren't expected to pay royalties on that (or even attribute the source): why can't the statement of a theme be regarded as a long quote?
The dividing line between "creative borrowing" and plagiarism is evidently rather thin.
So we come to the blues -- a topic that came up in the comments on this post on plagiarism. km used the example of blues to argue that "rules of stealing don't apply the same way in music". I argued that the blues are a good example because rock musicians are, in general, careful to credit composers of blues standards, and many a blues musician who was in hard times in the 1960s received a windfall this way.
This can become ridiculous: Cream's cover of Robert Johnson's "Cross road blues" (which they called "Crossroads") was nothing whatever like Johnson's version: only the words were taken from Johnson. Lynyrd Skynyrd's version of the same song -- both the singing and the guitar solos -- was a note-for-note repeat of Cream's version (even if it took 3 guitarists to reproduce Clapton's original, and their bassist was no Jack Bruce). But the royalties from Skynyrd's recording go to Robert Johnson's estate, not to Cream.
Partly, attribution is a matter of the law, and partly it's a matter of decency. (Skynyrd did publicly acknowledge Cream in their concerts, and this is reproduced in an alternate take on a recent release of "One more from the road", so I suppose they're absolved.) Bob Dylan has been accused, rather convincingly, of plagiarising others' lines in his two most recent albums. One can argue that he produced original work that just included "samples" from other works, creatively used; but it seems to me that he should have acknowledged his sources.
How much quoting without attribution is fair, how much quoting with attribution is fair, how much constitutes plagiarism? What the Times of India does is plagiarism by any definition, surely. What Kaavya Vishwanathan did looks very much like plagiarism. Is what Dylan did plagiarism? Kenny Barron? Handel?
I close with one of my favourite examples of suspicious and unacknowledged similarity, that I've never seen discussed elsewhere.
In Saki's short story "The Seven Cream Jugs", Mr and Mrs Pigeoncote are distressed at the visit of their cousin Wilfrid Pigeoncote, a kleptomaniac commonly known as "The Snatcher", at a time when their house is full of valuable silver-wedding presents including seven cream jugs. Their paranoia leads them to look into Wilfrid's suitcase and find a cream jug there, which they assume he stole from them; and they take it back. In fact, he had brought it as a possible wedding gift, and on finding it missing, he raises the alarm that there may be a thief in the house. And it turns out that he is not the "snatcher" but another cousin called Wilfrid, a diplomat. Eventually Mrs Pigeoncote explains things, out of Mr Pigeoncote's earshot, by telling Wilfrid that her husband is a kleptomaniac.
In P. G. Wodehouse's novel "Jeeves in the offing", a subplot of the book is Uncle Tom's silver cow-creamer, and the visit to Aunt Dahlia's house of Willie Cream, who Bertie and Aunt Dahlia believe is a kleptomaniac. So when they find the cow-creamer in his possession, Bertie and Aunt Dahlia steal it back -- only to find that he had bought the thing off Tom, and now wants to find the thief. Moreover, it turns out that Willie Cream is not the kleptomaniac (Wilfred) but his brother (Wilbert). Jeeves eventually sorts it out, in Bertie's absence, by telling everyone that Bertie is a kleptomaniac.
This surely meets the Kaavya standard for plagiarism. But I think the various associations here -- "Cream", "Wilfred", "silver" etc -- suggest unconscious plagiarism (even if that excuse has been demeaned by Kaavya): a conscious plagiarist would have changed those details. Moreover, I think Saki's copyright had lapsed by the time Wodehouse wrote his book, so there were no legal issues, only ethical ones.
(Saki seems to have been a fertile ground for ideas: another Saki idea -- a short story, "The Background", about a man whose back was tattooed by an artist who subsequently became famous, so that he went through life with a valuable and coveted painting on the skin of his back -- was pinched by Roald Dahl in his short story "Skin", though Dahl's version is much more macabre. Now, is that plagiarism?)
(caveat emptor -- the last four paragraphs were plagiarised from myself, in a mail I sent someone some months ago. Great artists reused their material too.)
Scientific plagiarism is a whole other can of worms. Since it's closer to my "real world", I'll leave that for later...