''No one,'' Hannah Arendt observed, ''has ever counted truthfulness as a political virtue.'' But why do politicians lie? What is the relationship between political lies and self-delusion? And how much organized deceit can a democracy endure before it ceases to function? Fifty years ago, the century''s greatest political theorist turned her focus to these questions in two seminal essays, brought together here for the first time. Her conclusions, delivered in searching prose that crackles with insight and intelligence, remain powerfully relevant, perhaps more so today than when they were written.