A study of the history of opinion is a necessary preliminary to the emancipation of the mind.

Keynes argues that intellectual freedom is not achieved merely by rejecting old ideas, but by understanding how those ideas arose, gained authority, and shaped what later generations take for granted. The “history of opinion” functions like a map of inherited assumptions: by tracing the genealogy of doctrines, one can see their contingency, interests, and blind spots. In this sense, historical study becomes a tool of critique—loosening the grip of conventional wisdom and enabling more independent judgment. The line also reflects Keynes’s broader habit of treating economic and political beliefs as historically situated rather than timeless truths, and it implies that reform in thought requires self-awareness about the traditions that formed one’s mental habits.