Isaiah berlin (1909–1997) was a Latvian-born political theorist and historian of political ideas. He was the Chichele Professor of Social and Political Theory at Oxford University between 1957 and 1967. Though the bulk of his writing had to do with the political ideas of thinkers of the Enlightenment and of the Counter-Enlightenment, he is perhaps best known among political philosophers for a relatively small number of essays that were published in the volume Four Essays on Liberty (Berlin 1969).

In these essays, Berlin defended a view of political life that emphasized the irreducible plurality of ends legitimately pursued by human agents. In Berlin’s view, pluralism puts paid to certain forms of political rationalism, according to which reason militates in favor of one of these values, or a small subset thereof. He viewed this kind of rationalism as insuficiently attentive to the plurality of ends, and as potentially politically noxious since the belief in a single rational end can fuel tyrannical political forms aimed at “freeing” human subjects from the hold that illusory desires and ends have upon them.

Pluralism is one of the grounds of Berlin’s preference for a negative as opposed to a positive conception of liberty. Negative liberty obtains when no one stands in the way of my doing what I want to do, whereas positive liberty has to do with the quality of my will, and with whether I truly want what I rationally ought to want. Some critics have urged that Berlin’s espousal of both pluralism and negative liberty is inconsistent, since a real pluralist would be indifferent as between the two conceptions (Gray 1996; Weinstock 1997).