Appropriation art has often been thought to support the view that authorship in art is an outmoded or misguided notion. Through a thought experiment comparing appropriation art to a unique case of artistic forgery, I examine and reject a number of candidates for the distinction that makes artists the authors of their work while forgers are not. The crucial difference is seen to lie in the fact that artists bear ultimate responsibility for whatever objectives they choose to pursue through their work, whereas the forger's central objectives are determined by the nature of the activity of forgery. Appropriation artists, by revealing that no aspect of the objectives an artist pursues are in fact built in to the concept of art, demonstrate artists' responsibility for all aspects of their objectives and, hence, of their products. This responsibility is constitutive of authorship and accounts for the interpretability of artworks. Far from undermining the concept of authorship in art, then, the appropriation artists in fact reaffirm and strengthen it.