Placement of both Hayek and Mill in the liberal tradition is suspect to many historians of political thought for various reasons. First, Mill also expressed socialist sentiments, so to classify him as a liberal has seemed inaccurate to some more right-inclined liberals. Second, Hayek is sometimes considered more a conservative by left-inclined liberals, and not in the liberal tradition as it has evolved. Nonetheless, Mill and Hayek were the two greatest liberals of the nineteenth and twentieth centuries.

Hayek's Journey: The Mind of Friedrich Hayek (2003) - Ch. 12 : Marx, Mill and Freud