Not too many people can point to a specific day when they sat down with a book and got up cured of the stupidities of youth. I can. I was 19. The book was "Four Essays on Liberty." The author was Isaiah Berlin. He died last week at 88.

Berlin was one of the great political philosophers of his time. Yet he never produced a single great tome. He left behind essays. But what essays. His most famous is "The Hedgehog and the Fox," a wonderfully imaginative division of the great thinkers of history into those who have one big idea (hedgehogs) and those who have many small ones (foxes).

Berlin was partial to foxes. He believed that single issues, fixed ideas, single-minded ideologies are dangerous, the royal road to arrogance and inhumanity. Against those who proclaimed they had found the one true path to political salvation, Berlin stood in the way, a champion of pluralism, the many-pathed way.

"Four Essays on Liberty" is his great argument for pluralism. Why was it such a powerful book? It came out in 1969. In 1969, to be young was heaven -- and to be seized with intimations of heavenly omniscience. It was a time of grand theories and grand aspirations -- liberation, revolution, historical inevitability -- and we children were mightily seduced.

The temptations were many. There was, of course, Marxism; for the masochistic, there was Trotskyism; for the near-psychotic, there was Maoism. And apart from Marxism and its variants, there was the lure of such philosophers as Rousseau, the great theorist of mass democracy and the supremacy of the "popular will."

In the midst of all this craziness, along comes Berlin and says: Look, this is all very nice, but what the monists -- the believers in the one true truth, Marx and Rousseau and (by implication) such Third World deities as Mao and Ho and Castro -- are proclaiming is not freedom. What they offer may be glorious and uplifting and just. But freedom is something very different. Freedom is being left alone. Freedom is a sphere of autonomy, an inviolable political space that no authority may invade.

In fact, said Berlin, these other "higher" pseudo-freedoms peddled by the monist prophets are very dangerous. They proclaim one true value above all else -- equality in Marx, fraternity in Rousseau -- and in the end the individual with his freedom is crushed underfoot. Heads roll. Millions of them.

And another thing, said Berlin: Historical inevitability is bunk, a kind of religion for atheists.

And one more thing, he said (in the fourth and final essay of the book): The true heart of the liberal political tradition is the belief that no one has the secret as to what is the ultimate end and goal of life. There are many ends, each deserving respect, and it is out of this very pluribus that we get freedom.

I read this book and a great fog -- made of equal parts youthful enthusiasm, hubris and naivete -- lifted. I was forever enlisted on the side of limited, constitutional government -- flawed as it was and despised at the time as "the system."

Berlin's argument seems blindingly obvious now. But the anti-"system" ravings of, say, the Unabomber, which seem grotesque today, were common fare on the campuses of 1969. Today history has buried Marxism's pretensions. In 1969, when history had not quite played itself out, Berlin's book was a tonic.

It was not without its flaws. It was brilliant in deconstructing the political romantics. But it did have its logical conundrum. Philosopher Leo Strauss, in his essay "Relativism" surgically exposed the central paradox of Berlin's position: that it made pluralism -- the denial of one supreme, absolute value -- the supreme, absolute value.

This paradox and Berlin's fecund, restless mind -- which moved from one idea to another (often in the same sentence!) -- prevented him from establishing a grand intellectual edifice of his own. He remained forever a fox. But just as there are hedgehogs and foxes, there are creators and there are curers. Berlin was one of our great curers.

"Four Essays" is available everywhere. Buy it. Make your children read it before they go to college, the last redoubt of romantic neo-Marxism. If they think the book is obvious, you have raised them well. If they don't, Berlin will challenge their complacency.

And keep one copy at home. The idea of limited government has triumphed. But the moment may not last. The pluralism Berlin championed will be challenged again. Whether by religious fundamentalism, by some reconstructed Marxism, or by an ideology whose outlines and ugliness we cannot even imagine today, it will be challenged. When that day comes, Berlin and his "Four Essays" will be needed again.