"Liberalism," New Studies in Philosophy, Politics,  Economics and the History of Ideas, Routledge & Keagan Paul, London and Henley, 1982 [1978], pp. 119-151.

Excerpt:

“The term is now used with a variety of meanings which have little in common beyond describing an openness to new ideas, including some which are directly opposed to those which are originally designated by it during the nineteenth and the earlier parts of the twentieth centuries. What will alone be considered here is that broad stream of political ideals which during that period under the name of liberalism operated as one of the most influential intellectual forces guiding developments in western and central Europe. This movement derives, however, from two distinct sources, and the two traditions to which they gave rise, though generally mixed to various degrees, coexisted only in an uneasy partnership and must be clearly distinguished if the development of the liberal movement is to be understood.

The one tradition, much older than the name ‘liberalism’, traces back to classical antiquity and took its modern form during the late seventeenth and the eighteenth centuries as the political doctrines of the English Whigs. It provided the model of political institutions which most of the European nineteenth‑century liberalism followed. It was the individual liberty which a ‘government under the law’ had secured to the citizens of Great Britain which inspired the movement for liberty in the countries of the Continent in which absolutism had destroyed most of the medieval liberties which had been largely preserved in Britain. These institutions were, however, interpreted on the Continent in the light of a philosophical tradition very different from the evolutionary conceptions predominant in Britain, namely of it rationalist or constructivistic view which demanded a deliberate reconstruction of the whole of society in accordance with principles of reason. This approach derived from the new rationalist philosophy developed above all by René Descartes (but also by Thomas Hobbes in Britain) and gained its greatest influence in the eighteenth century through the philosophers of the French Enlightenment. Voltaire and J.‑J. Rousseau were the two most influential figures of the intellectual movement that culminated in the French Revolution and from which the Continental or constructivistic type of liberalism derives. The core of this movement, unlike the British tradition, was not so much a definite political doctrine as a general mental attitude, a demand for an emancipation from all prejudice and all beliefs which could not be rationally justified, and for an escape from the authority of ‘priests and kings’. Its best expression is probably B. de Spinoza’s statement that ‘he is a free man who lives according to the dictates of reason alone’.”

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