nettime: There is a good description of art appropriation from the Detournement movement in 1950s to intellectual property being the “Oil of the 21st century”:
In a post-industrial society production is no longer confined to material goods (such as steel and coal) but increasingly extends to immaterial goods. However, a significant difference exists between the two: immaterial goods like knowledge and information can be reproduced without impairment, which is not the case with material goods. But in order to be able to function within a value chain, the distribution of these immaterial goods must be restricted - namely with the aid of patent, copyright and trademark law.