Henry Hardy at the TLS:
Berlin’s absorption in the history of ideas dates back almost to the beginning of his academic career. In 1933 he was commissioned to write a book on Karl Marx, which was published in 1939 and is still in print today. His reading of Marx and Marx’s predecessors, especially the philosophers of the Enlightenment, and even more their opponents, the “Counter-Enlightenment” as he called them, fuelled his thought for the rest of his life.
In the Enlightenment he finds the most complete expression of a philosophical view that he traces back at least to Plato: the view that, properly managed and understood, human life and society can be harmonious and coherent, all moral and political questions finally answered, all values frictionlessly reconciled, and conflict and misery eliminated. (The enormous implausibility of such a view testifies to the ability of philosophers to espouse beliefs known to be false by anyone with a modicum of common sense.) In the eighteenth century this belief was reinforced by the success of the scientific revolution, which created the expectation that human affairs, like the natural world, could be explained in scientific terms.