 By the early 1950s Berlin’s central beliefs had crystallised from the confluence of his philosophical preoccupations, historical studies, and political and moral commitments and anxieties; and his major ideas were either already fully formed, or developing. Such essays of the late 1950s as Two Concepts of Liberty served as the occasion for a synthesis and solidification of his thoughts. Berlin had always been a liberal; but from the early 1950s the defence of liberalism became central to his intellectual concerns. This defence was, characteristically, closely related to his moral beliefs and to his preoccupation with the nature and role of values in human life. In the early 1960s Berlin’s focus moved from the more political concerns that occupied him in the 1950s to an examination of the nature of the humanities. Throughout the 1950s and 1960s he was working on the history of ideas, and from the mid 1960s nearly all of his writings took the form of essays in this field, particularly on the Romantic and reactionary critics of the Enlightenment. In the final decades of his life Berlin continued to refine and re-articulate his ideas, and particularly his formulation of pluralism; but his course was set, and he appears to have been little affected by later intellectual developments.