 Their 2013 book "The Inessential Indexical" argues that the phenomena which, for example, John Perry and David Lewis think show the importance of indexical representation of the self and time can be accounted for using resources already available in the philosophy of language and thought.Cappelen has also authored, or co-authored, important books on the debate between contextualists and relativists ("Relativism and Monadic Truth", with John Hawthorne), and on quotation ("Language Turned on Itself" with Ernest Lepore).Some of his papers co-written with Ernie Lepore are collected in "Liberating Content".