Combining historical analysis with contemporary observation, Susan Jacoby dissects a new American cultural phenomenon--one that is at odds with our heritage of Enlightenment reason and with modern, secular knowledge and science. With mordant wit, she surveys an anti-rationalist landscape extending from pop culture to a pseudo-intellectual universe of ''junk thought.'' Disdain for logic and evidence defines a pervasive malaise fostered by the mass media, triumphalist religious fundamentalism, mediocre public education, a dearth of fair-minded public intellectuals on the right and the left, and, above all, a lazy and credulous public.

Jacoby offers an unsparing indictment of the American addiction to infotainment--from television to the Web--and cites this toxic dependency as the major element distinguishing our current age of unreason from earlier outbreaks of American anti-intellectualism and anti-rationalism. With reading on the decline and scientific and historical illiteracy on the rise, an increasingly ignorant public square is dominated by debased media-driven language and received opinion.

At this critical political juncture, nothing could be more important than recognizing the ''overarching crisis of memory and knowledge'' described in this impassioned, tough-minded book, which challenges Americans to face the painful truth about what the flights from reason has cost us as individuals and as a nation.