"Blurred Lines" may be viewed as an example of what is known as contrafact and it isn't even strict contrafact at that. When an artist takes a harmonic progression or in this case, a "groove" from one composition and replaces the melody and lyrics with their own, the result is called a contrafact. Contrafacts have been around for a long time and are legal and acceptable. The vast majority of jazz standards from the bebop era were written this way in order to "avoid" copyright infringement.

For example "Ornithology" uses the chord progression of "How High the Moon", "Ko-ko" uses the chords from "Cherokee" and "Moose the Mooche" (along with dozens of other jazz compositions) uses George Gershwin's "I Got Rhythm" as it's chief inspiration. The chords to "I Got Rhythm" are among the most "stolen" (if that's what you want to call it) in all of jazz.

There are also some contemporary contrafacts. For example, try listening to the Isley Brother's "Choosey Lover" and tell me it doesn't remind you of "Devotion" by Earth Wind and Fire. While this also may not be a strict example of contrafact, it sounds like one song inspired the other and that they not only share very similar chord progressions but similar melodies too. Yet there is no songwriting credit given to Maurice White for "Choosey Lover". Are the Isleys talentless hacks because of this? Of course not. This is a example of one artist hearing a great song and being inspired to write another great song.

An musical artist cannot copyright a chord, harmonic progression or a rhythm. Those are basic tools that all musical artists use to create. Think of all those similar sounding 808 drum patterns that defined the Miami hip hop sound of the '80s and '90s or all of the II-V-I progressions heard in countless songs spanning a wide variety of genres. A musical artist can however, copyright an original melody, lyric or musical arrangement. They can also copyright a sound recording of their original lyric, melody or musical arrangement. Robin Thicke would've had to make an "exact" copy of the lyrics, melody, musical arrangement or sample a part from the original recording of "Got To Give It Up" somewhere in his song in order to be held liable for infringement.

While "Blurred Lines" may be considered a knockoff for capturing the "feel" of Gaye's classic, it's easy to tell (for me anyway) that the two songs are not identical. The lyrics don't match. The melodies don't match either. There are no samples from a Marvin Gaye recording used in Thicke's song and if you scored the musical arrangements out on paper from both songs, they would be different in practically every way. The only notable similarity between the two is the rhythm of the keyboard part (and possibly the song key though I haven't verified) but the chord progressions between the two are not exact and neither are the basslines.

You may not like Robin Thicke's singing and you may even hate his new song but in my opinion, he has done nothing wrong ethically or legally and you can't expect everyone to come up with a song like "Babylon Sisters". If anything, Robin Thicke has only reminded some of us what a great song "Got To Give It Up" is while creating an opportunity for a new generation of curious listeners to explore and appreciate this song and others in Marvin Gaye's great catalog. This is what hip hop started out doing before the law got involved and look at it now.

I'm really quite surprised and somewhat saddened by some of the discussions that I have read in regards to this matter. I thought we would know better but then again, this "is" America circa 2013...