May is Washington's mellowest month, a season of azalea and the Jefferson Lecture. That lecture leavens the deadening day-to-dayness of Washington events with thoughts never out of season. The lecture, funded by the National Endowment for the Humanities, is a tribute to the maturity of the government, which has institutionalized an intellectual pause that refreshes. And there was special poignancy to this year's lecture because of the winding path by which Leszek Kolakowski came to that podium.

On American campuses, the 1960s were years of living frivolously. Many "radicals" found mere speech inadquate to the expression of their thoughts, and so they seized the dean's office and smoked his cigars. In Poland, dissent by "mere speech" was more dangerous.

When the fever of 1968 ignited student protests there, the regime dismissed Kolakowski from his teaching position at the University of Warsaw. His words had contributed to the shaking of the regime. He has not been home since, and now teaches at Oxford and the University of Chicago. In his lecture, he taught a lesson about the philosophic prerequisites of pluralism.

Kolakowski's theme was sobered Jeffersonianism. He accepts the Enlightenment belief in diversity, but the belief tempered by the 20th-century experience with totalitarianism. The harshness of contemporary history has made Kolakowski cosmopolitan, suspended between national cultures, yet he praises immersion in the particularities of national histories. Having honed his mind on the abrasiveness of a closed society, he is qualified to warn that maintenance of an open society involves more than mere toleration of diversity.

The state cannot be "neutral" regarding fundamental values. In pluralist societies, ideas are governed by the rules of the market. The consumer is sovereign. However, the freedom to enter the intellectual marketplace is the result of an ideological choice and institutional arrangements. Society and its collective will, the state, cannot be neutral about them. Society should be partisan on behalf of the prerequisites of pluralism. Three prerequisites, says Kolakowski, are revisions of the thinking of Jefferson's age.

The Enlightenment taught that beliefs about good and evil are culture-bound and historically relative, and that to believe otherwise breeds fanaticism. But the good seed of temperate skepticism produced the dangerous fruit of dogmatic relativism. The values of pluralism and tolerance came to seem as relative as their opposites. And it is a short step from indiscriminate skepticism to paralysis: we are imperfect, so we have no moral standing to reproach evil.

Enlightenment optimism taught the compatibility of all good things -- peace, justice, freedom, equality. But Kolakowski reminds that for 40 years Europe's peace has been based on the glaring injustice of the subjugation of the eastern part of the continent.

Second, Enlightenment philosophy, says Kolakowski, stressed too much the socialization of the individual, producing an "uncertain and conceptually fragile status of human personality." The belief that the individual is "entirely society-made" means that "I" is a pronoun to which no morally important reality corresponds. That belief produces the notion that "society" is responsible for everything, "I" for nothing.

It also leaves us "conceptually defenseless" against totalitarianism. Today's world conflict, says Kolakowski, is not just the competition of large nations for enlarged influence, it is a clash of civilizations. At stake is "humanity as we have known it." This is not because "Sovietism" is militaristic and aggressive, which of course it is. Rather, the stakes are so high "because of its educational goals," which are to reduce people to replaceable parts of a state machine.

Kolakowski says the third needed revision of the Enlightenment legacy concerns historical consciousness. Enlightenment confidence became hubris, dismissing the past as a heap of ignorance and superstition. What we learn from history is not technical guidance for goverance, like consulting a manual to fix a machine. We study history to learn who we are. However, a sense of history is practical in this sense: the most consequential leaders often are those -- Churchill, de Gaulle -- most conscious of being immersed in a stream of history.

Kolakowski's angular face often has the expression of a hawk that has just heard an amusing jest at the expense of hawks. He once wrote that "Philosophers neither sow nor harvest, they just move the soil around." Not true. Philosophers cannot know the full distant harvest of the thoughts they sow. But the harvest is real. And the fact that our government, through the Jefferson Lecture, honors thinkers of Kolakowski's stature suggests that the seeds do not fall here on stony ground.