In political science, the label "radical" denotes "one who desires extreme change of all or part of the social order." (Britannica Deluxe CD2000). The term is said to have been used by the English parliamentarian Charles Fox who, in 1797, demanded a "radical reform" of the electoral system amounting to universal male suffrage. It was thenceforth applied to any who lobbied for electoral reform.

The passage of the Reform Act of 1867 gave the vote even to workers and the Radicals, having been strenuous in their efforts on behalf of the working classes, thereby earned a deeply loyal following; British trade unionists from 1874 until 1892, upon being elected to Parliament, never considered themselves to be anything other than Radicals.

English Radicals derived much of their ideas from 'philosophical radicals', particularly John Stuart Mill who held that right actions were to be measured in proportion to the greatest good they achieved for the greatest number.

Likewise, in France, radicalism meant support for democratic ideals - in this case, republicanism. The republicans called themselves radicals, espousing anything other than a constitutional monarchy being (in theory, at least) illegal. But, a breakaway group, envisioning themselves as heirs to 1789, began calling themselves Radicals, forming the Radical-Socialist party just before the turn of the century.