Martin Jay tackles a question as old as Plato and still pressing today: what is reason, and what roles does and should it have in human endeavor? Applying the tools of intellectual history, he examines the overlapping, but not fully compatible, meanings that have accrued to the term "reason" over two millennia, homing in on moments of crisis, critique, and defense of reason.

After surveying Western ideas of reason from the ancient Greeks through Kant, Hegel, and Marx, Jay engages at length with the ways leading theorists of the Frankfurt School--Horkheimer, Marcuse, Adorno, and most...