FOR SEVERAL DECADES, Sir Isaiah Berlin, intellectual historian and political theorist, has enjoyed I will not say an underground but a rather specialized reputation. An inimitable raconteur, generous teacher, brilliant and high-velocity lecturer, he has long been admired, indeed loved by his students at Oxford and elsewhere for his wit, his erudition, his principled unostentatious humanity. But apart from a splendidly lucid, balanced and widely read short biography of Karl Marx, a controversial, equally short set of essays on liberty, and a famous study of Tolstoy's philosophy of history, The Hedgehog and the Fox, just as short, he seemed to have published little, and that, usually, in out-of-the-way periodicals.

Now that he is entering his seventies and Henry Hardy is bringing together Berlin's essays and lectures in four volumes, it appears that he has in fact written a good deal. Many of Berlin's admirers have thought of him as a speaker rather than as a writer, and it is true that to read him is to hear his voice. But fortunately he has committed to print far more than was generally realized. The first volume of his "Selected Writings," Russian Thinkers, collected some memorable pieces on figures like Alexander Herzen and Ivan Turgenev. The second volume, Concepts and Categories, showed Berlin is quite another, but no less happy role: the accomplished technical philosopher. Oxford has left its imprint on Isaiah Berlin, just as he has left his imprint on Oxford.

Against the Current, the volume just published, presents Berlin in what is perhaps his most familiar guise, that of the historian of political ideas. These 13 pieces, intelligently, almost reverently introduced by Roger Hausheer, add up to a substantial book. They range from Nicolo Machiavelli to Georges Sorel, from Montesquieu to Moses Hess, and (in new visits to territory that Berlin has already made his own) from Vico to Herzen and Marx. Perhaps the most surprising item, testifying to Berlin's celebrated devotion to opera, is a delightful piece, little more than a vignette, on "The 'Naivete' of Verdi," in which he pays tribute to Verdi's utter naturalness, a quality that Schiller had called, without disparagement, "naive." Verdi's "assured place" in high art, he tells us, "is a symptom of sanity in our time."

At first glance this may appear to be a somewhat miscellanous collection, and it is true that Berlin wrote these essays for a variety of occassions. But they are unified by the powerful convictions and penetrating perceptions of their author. In all of them, the scholarship is impeccable; Berlin's command of the secondary literature is as complete as that of the sources themselves. Beyond that there is Berlin's gift, no less evident on the printed page than in the lecture hall, for entering the cluster of ideas he is analyzing and for presenting them with a clarity that leaves his audience not merely dazzled but a little wiser than before.

But there is yet another agent of unification, which ties together the essays in this volume and links them to the rest of his work: a devotion to decency, to freedom, to the variety and the dignity of human experience. Berlin never rants, and his passion for liberty and pluralism never interferes with his self-assigned task as expounder and interpreter. That is why Roger Hausheer is perfectly justified to conclude his introduction by picking up Berlin's accolade to Verdi and applying it to the "growing interest" in Berlin's writings: it is, as he felicitously puts it, "a symptom of sanity in our time." We can use as much of Isaiah Berlin's kind of sanity as we can get.