'One is a Lonely Number': on the Logic of Communication Johan van Benthem Abstract: 'One is a Lonely Number': on the logic of communication Johan van Benthem Abstract: Logic is not just about single-agent notions like reasoning, or zero-agent notions like truth, but also about communication between two or more people. What we tell and ask each other can be just as logical as what we infer in Olympic solitude. We show how such interactive phenomena can be studied systematically by merging epistemic and dynamic logic.