Seeing things plain, not lying to oneself, not subscribing to the delusions of others – these virtues, seemingly so simple, prove in life difficult to achieve and tricky to exercise. An inevitable imitative pressure assimilates people to one another so that mere opinion, received but never vetted, comes to function as a surrogate reality, in the cave-like error of which people stumble about their errands in a lurching mockery of witting behavior. The ancients worried about false or second-hand judgment (doxa) or about superstition. Modern people must grapple with ideology. The critique of ideology is the single most important exercise...