Sidney Hook is considered by many to be America's most influential philosopher. An earlier defender of Marxism, he became its most persistent critic, especially of its totalitarian and revolutionary manifestations. A student of John Dewey's pragmatism, Sidney Hook has written extensively about most of the live moral, social and political issues of the day. He has known and debated many of the leading thinkers of the twentieth century, such as Max Eastman, Bertrand Russell, Albert Einstein, Jacques Maritain, Mortimer Adler, Robert Hutchins, Paul Tillich, Noam Chomsky, and John Kenneth Galbraith.