In all of its varieties, traditional liberalism is a universalist political theory. Its content is a set of principles which prescribe the best regime, the ideally best institutions, for all mankind. It may be acknowledged — as it is, by a proto-liberal such as Spinoza — that the best regime can be attained only rarely, and cannot be expected to endure for long; and that the forms its central institutions will assume in different historical and cultural milieux may vary significantly. It will then be accepted that the liberal regime's role in political thought is as a regulative ideal, which political practice can hope only to approximate, subject to all the vagaries and exigencies of circumstance. Nonetheless, the content of traditional liberalism is a system of principles which function as universal norms for the critical appraisal of human institutions. In this regard, traditional liberalism — the liberalism of Locke and Kant, for example — represents a continuation of classical political rationalism, as it is found in Aristotle and Aquinas, where it also issues in principles having the attribute of universality, in that they apply ideally to all human beings.