America values dissent. It tolerates, encourages, and protects it. But what is this thing we value? That is a question never asked. “Dissent” is treated as a known fact. For all that has been said about dissent – in books, articles, judicial opinions, and popular culture – it is remarkable that no one has devoted much, if any, ink to explaining what dissent is. No one has attempted to sketch its philosophical, linguistic, legal, or cultural meanings or usages. There is a need to develop some clarity about this phenomenon we call dissent, for not every difference of opinion, symbolic gesture, public activity in opposition to government policy, incitement to direct action, revolutionary effort, or political assassination need be tagged dissent. In essence, we have no conceptual yardstick. It is just that measure of meaning that On Dissent offers.