Drawing on positioning theory, this paper presents a historical sketch of changes in how intellectuals engage with their publics. It starts with the simple observation that in the first half of the twentieth century public intellectuals tended to be philosophers, but their public engagement has steadily declined since then. Increasingly, social and natural scientists have taken a more prominent role. The paper attempts to explain this change, showing how it reflects a more substantial shift away from the authoritative public intellectual. Epitomised by Sartre and Russell, authoritative public intellectuals are generalists whose cultural capital enables them to speak out with moral vigour about a wide range of social and political issues without ever exhibiting expertise in any of them. The paper identifies the major sociological factors which have made it increasingly difficult to act as authoritative public intellectuals without losing credibility.