Are knowledge claims indexical? (David Lewis, Stewart Cohen, and Keith DeRose)

David Lewis, Stewart Cohen, and Keith DeRose have proposed that sentences of the form "S knows P" are indexical, and therefore differ in truth value from one context to another.' On their indexical contextualism, the truth value of "S knows P" is determined by whether S meets the epistemic standards of the speaker's context. I will not be concerned with relational forms of contextualism, according to which the truth value of "S knows P" is determined by the standards of the subject S's context, regardless of the standards applying to the speaker making the knowledge claim. Relational contextualism is a form of normative relativism. Indexical contextualism is a semantic theory. When the subject is the speaker, as when "S" is the first person pronoun "I," the two forms of contextualism coincide. But otherwise, they diverge. I critically examine the principal arguments for indexicalism, detail linguistic evidence against it, and suggest a pragmatic alternative.