The sensitivity condition on knowledge emerges out of a simple but highly attractive idea: whether S's belief that p amounts to knowledge depends on whether S would have so believed had it been false that p. This chapter describes a belief that makes true the sensitivity conditional in SEN, the conditional that if p were false, then S would not believe that p via M, as classically sensitive, or c-sensitive for short. It is helpful to start the discussion by assuming that the sensitivity condition on knowledge requires classic-sensitivity, that is, by assuming that c-sensitivity is a necessary condition on knowledge. The chapter assumes a sensitivity account that consists in a conjunction of three claims: SEN, the Sufficiency Thesis, and the claim that M (TGEN) is the proper way to individuate the belief-forming method involved in testimony cases. Such an account entails what it calls the testimony/classicalsensitivity biconditional, or TCS-biconditional.