There's a lot of reasons why it is important to credit people for their work, although the only one that seems to...

There's a lot of reasons why it is important to credit people for their work, although the only one that seems to motivate action is money. However, this and the Robin Thicke/Marvin Gaye thing are really making me wonder about where we are and what really constitutes plagiarism versus what a lawyer can convince people is too similar.

For example, if this attitude had been prevalent during the Baroque and Classical eras of classical music, which was the popular music at the time, we wouldn't have half of the great music we did. We certainly wouldn't have had a tremendous, bitingly sarcastic collection of music, as well as written commentary (they really knew how to do snark in those days). Taking something a colleague/competitor had done and deliberately taking it in whole or in part and then going them one better, or reconfiguring it to mock them, or just quoting it as a tribute to them was an acceptable and encouraged thing to do.  

So you could say that even if "Blurred Lines" was strongly reminiscent of "Got to Give it Up", or inspired by it, or even used recognizable snippets, that it was just a tribute. Not a ripoff that owed you money. It would even have mattered more in the past, because musicians and composers simply did not make money the way they do now. Exceptions were vanishingly rare. Plus, it was free publicity for the quoted.

I can think of modern examples, too. More esoteric ones, like the main love theme in the score to the movie Like Water for Chocolate, which is harmony for harmony the "Liebestod" from Wagner's Tristan und Isolde, or well known ones, like John Williams' score for Star Wars and Gustav Holst's The Planets. Afaik, nobody's trust or estate filed lawsuits over these. In fact, half of the fun of this for music geeks is going, hey! I know that bit! It's from [insert here]!

I'm sure there's a way to parse some level of difference, but I'm having trouble doing it. I really am. 

http://www.theguardian.com/music/2016/apr/12/stairway-to-heaven-led-zeppelin-copyright-lawsuit
http://www.theguardian.com/music/2016/apr/12/stairway-to-heaven-led-zeppelin-copyright-lawsuit