It's an obvious enough observation that the standards that govern whether ordinary speakers will say that someone knows something vary with context: What we are happy to call "knowledge" in some ("low-standards") contexts we'll deny is "knowledge" in other ("high-standards") contexts. But do these varying standards for when ordinary speakers will attribute knowledge, and for when they are in some important sense warranted in attributing knowledge, reflect varying standards for when it is or would be true for them to attribute knowledge? Or are the standards that govern whether such claims are true always the same? And what are the implications for epistemology if these truth-conditions for knowledge claims shift with context? Contextualism, the view that the epistemic standards a subject must meet in order for a claim attributing "knowledge" to her to be true do vary with context, has been hotly debated in epistemology and philosophy of language during the last few decades.
In The Case for Contextualism Keith DeRose offers a sustained state-of-the-art exposition and defense of the contextualist position, presenting and advancing the most powerful arguments in favor of the view and against its "invariantist" rivals, and responding to the most pressing objections facing contextualism.