Admirers and critics agree that Berlin's distinction between positive and negative liberty remains, for better or worse, a basic starting-point for theoretical discussions of the meaning and value of political freedom.
Berlin had always been a liberal; but from the early 1950s the defence of liberalism became central to his intellectual concerns. Berlin's central beliefs had emerged out of 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 ‘50s as ‘Two Concepts of Liberty’ served as the occasion for a synthesis and solidification of his thoughts.
The republication in thematic collections of Berlin's numerous essays, beginning with Four Essays on Liberty (1969) and Vico and Herder (1976), and continuing at an increased pace from 1978 under the general editorship of Henry Hardy, revealed as a central dimension of Berlin's thought his advocacy of the doctrine of value pluralism.
While Berlin sometimes suggests that values are human creations, at other times he seems to advance what amounts almost to a theory of natural law, albeit in minimalist, empirical dress. In such cases he suggests that there are certain unvarying features of human beings, as they have been constituted throughout recorded history, that make certain values important, or even necessary, to them. This view of the origin of values also comes into play in Berlin's defence of the value of liberty, when he suggests that the freedom to think, to enquire and to imagine without constraint or fear is valuable because human beings need to be able to have such mental freedom; to deny it to them is a denial of their nature, which imposes an intolerable burden.
Negative liberty Berlin initially defined as freedom from, that is, the absence of constraints on the agent imposed by other people. Positive liberty he defined both as freedom to, that is, the ability…