The NYTimes’ Freakonomics blog uses the subject of poetry criticism to tackle fair use:
In a recent article, the poetry critic of the New York Times complained that to do poetry criticism right, it’s often necessary to quote extensively from a poem. Indeed, in the case of a short poem, it might be helpful to readers to copy the whole thing. But, the critic said, this can’t be done because it might run afoul of copyright law.
It is true that copyright law prohibits the unauthorized copying of any substantial part of someone’s poem, song, or other work.…Is this a good policy? From an economic perspective, no.
The reason this is bad policy, however widely discussed, bears repeating:
Use of a small bit of someone else’s creative work to build a new creative work rarely harms the economic interests of the first copyright owner, because most “derivative” works do not directly compete with the original.
Every creator builds on what came before, and such building usually doesn’t “compete” with that earlier work in any economic sense. Creating legal fear and uncertainty about building on the past, however, is quite effective in limiting the creation of new works in the present.