> You would violate Rowling's copyright, for instance, if you took a Harry Potter book, outlined the plot (even with character and place names changed), and wrote a new novel from scratch using that outline.
Terry Brooks might be surprised to hear this, as he seems to have been safe from the notoriously litigious Tolkien estate. Try reading The Lord of the Rings sometime, then read The Sword of Shannara (accurately described as "especially blatant in its point-for-point correspondence" [1]).
Again, though, all that's only relevant if you're interested in the actual state of the world.
[1] http://en.wikipedia.org/wiki/The_Sword_of_Shannara#Sword_and...
However, contrary to popular belief, trademarks do not prohibit others using your trademarks in their writing. They prohibit others using your trademarks deceptively or in a way likely to cause confusion. Which means you don't have the same ability to prevent someone from using your trademark in the title or content of their book, that you have to prevent them from using copyrighted material in their book.
So an author can force a film company to switch all it's employees to rainbow colored forks in their family homes and the film company has two options : comply, or find another book to make a movie from.
This is similar to an EULA. You are in no way forced to sign the EULA. But there's nothing else giving you the right to use the software. So you have one of two choices : agree to the EULA, or find another piece of software.
Another quirk: copyright law also views copies of sufficiently important elements (like characters/setting/etc. which are clearly taken from another work) as a copyright violation, even if the story is different; fanfic is technically a copyright violation.
Are you sure about that? What is the cutoff? Hemingway's six-word story is certainly copyrightable.
Nobody can copyright a three word phrase. [edit: almost never, see [1]]
Copyright also applies if you copy enough story elements, but that doesn't apply because 50 Cent's movie is not in any meaningful way a copy of Achebe's story. And if that were the case, even changing the title completely wouldn't avoid infringement. You would violate Rowling's copyright, for instance, if you took a Harry Potter book, outlined the plot (even with character and place names changed), and wrote a new novel from scratch using that outline.
"The novel with the said title was initially produced in 1958 (that is 17 years before [50] was born)," replied his lawyers, according to Naijan. "[It is] listed as the most-read book in modern African literature, and won't be sold for even £1bn."
I think this was IP bullying by Achebe's legal team (if were laywers at all). They claim to have a monopoly to use the very generic title (even when separated from the underlying story), and when offered a lot of money (I'd love to hear 50 Cent's lawyers reason for offering a million dollars to use that title), they make a category error, confusing rights to the book itself with rights to a fairly generic title.
[1] http://fairuse.stanford.edu/2003/09/09/copyright_protection_...