This article identifies a distinct strand of 20th-century liberal thought that was exemplified by Isaiah Berlin, Raymond Aron and, to a lesser extent, Karl Popper. I offer a stylized account of their common ideas and shared political sensibility, and argue that their primarily negative liberalism was a variety of what Judith Shklar called the `liberalism of fear' — which put the imperative to avoid cruelty and atrocity first. All three founded their liberalism on a `politics of knowledge' that was directed primarily against Marxist philosophies of history and less against the idea of bureaucratic planning, as, in contrast, was the case with Friedrich von Hayek's thought. Moreover, all three subscribed to more or less explicit versions of value pluralism, and claimed that, in the circumstances of modernity, Weber's `clash of values' was exacerbated and required a particularly prudential approach to politics; this prudential management of value conflicts in turn was best entrusted to cultivated bureaucratic elites. All shared an image of a tolerant and humane society — essentially an idealized version of Britain — but said perhaps too little on the question how societies without the appropriate traditions of moderation and compromise were to be liberalized.