Abstract

This chapter contains sections titled: The use of epistemic modalities is intended as a development of the earlier account of discriminability, not an alternative to it; they should therefore be understood in terms of knowledge rather than certainty. The non‐transitivity of intentional indiscriminability is a robust phenomenon in epistemic modal logic. For KT5 is one of the strongest modal systems of philosophical interest; on the current reading, it presents facts about cognition as themselves entirely open to cognition. In KT5, we cannot distinguish between non‐intentional indiscriminability and identity. At least two responses to this fact are possible. We can retreat from KT5 to a weaker system such as KT4, or we can treat indiscriminability as intentional within KT5. The failure of intentional indiscriminability to be transitive in KT5 can be traced to the subject's inability to tell which object some of the presentations present.