Isaiah Berlin's celebrated radio lectures on six formative anti-liberal thinkers were broadcast by the BBC in 1952. They are published here for the first time, fifty years later. They comprise one of Berlin's earliest and most convincing expositions of his views on human freedom and on the history of ideas--views that later found expression in such famous works as "Two Concepts of Liberty," and were at the heart of his lifelong work on the Enlightenment...