Though some of Sir Isaiah's best-known essays were included in the previous two volumes of his collected essays (Russian Thinkers and Concepts and Categories), this third of four scheduled volumes contains the essence of Berlin's scholarly contribution because all his writing is deeply involved with the history of ideas. If he has a single guiding principle, it is that the search for a final truth is illusory and dangerous, and that human existence is culturally, historically, and therefore relatively constituted. Not surprisingly, then, his touchstone is Vico, the 18th-century Italian philosopher who rejected the notion that the methods of the natural sciences--particularly mathematics--could yield definitive results when applied to the realm of social life, where what is true for one culture and historical epoch is not necessarily true for another. Aside from two essays specifically on Vico, Berlin explores the same theme in pieces on Machiavelli, Montesquieu, and various lesser-known thinkers of the "counter-Enlightenment." In all of these, Berlin treads a narrow path bordered by various irrationalist currents, but his step is sure and he knows just where he is going in extolling the virtues of intellectual temperance and pluralism against the excesses of pseudo-scientific rigidity. Other essays deal with problems of Jewish identity, centering on the writings of Moses Hess, a 19th-century socialist and Zionist, and on a comparison of the existential similarities of Benjamin Disraeli and Karl Marx. The issue of cultural identity is also taken up in essays on Alexander Herzen and George Sorel, and in a final piece on nationalism as a force to be reckoned with. Throughout, Sir Isaiah is mapping our own cultural and historical relatedness and showing us the implicit "relevance" of the history of ideas to our time. The essays are elegantly written, one and all, by a master of the genre who is also one of the true intellectuals living today.