A compelling defense of free speech against its new enemies, who range from the mosques of Iran to the groves of American academe. In place of Justice Holmes's old standard of truth competing in ``the marketplace of ideas,'' Rauch (The Outnation, 1992--not reviewed; contributing editor to National Journal) substitutes a new one: that of ``liberal science.'' Formulated by skeptical epistemologists like Hume and Locke in reaction to the authoritarian regulation of knowledge advocated by Plato, liberal science sorts through the hurly-burly of conflicting claims of truth, marginalizing those that cannot pass scrutiny while accepting that even today's accepted truth may need to be revised tomorrow. But after years of nurturing the spirit of intellectual freedom and the pursuit of knowledge, this principle recently has been shaken, with the defining moment being Western governments' weak-kneed reaction to the 1989 death threat made by the Ayatollah Khomeini against Salman Rushdie. Rauch divides challengers to free speech into three camps: ``fundamentalists,'' who believe truth is obvious and not to be questioned; ``egalitarians,'' who think that the beliefs of all sincere people deserve equal respect; and ``humanitarians,'' who hold that one must never offend. But whether they are Moslems enraged at negative portrayals of Islam, creationists pressing to have their theory taught along with evolution, or minorities imposing university codes against ``hate speech,'' all these groups wish to revive the Inquisition notion that ``people who hold wrong and hurtful opinions should be punished for the good of society.'' Rauch's strength here lies in his relentless insistence that liberal science, though hurtful at times, is the best means of advancing knowledge and avoiding ``herdthink.'' Rauch, Jewish and gay, calls not just for toleration but for ``the hard self-discipline which requires us to live with offense.'' A powerful salvo in the war over political correctness--and a ringing reaffirmation of the principles of free thought as conceived by Locke, John Stuart Mill, and others.