Aristotle's practical philosophy has often been considered as the paradigm of a non-deontological conception—that is, one in which there is not a concept of rule as a criterion universally determining what individuals shall do. Yet this image needs to be severely rectified when we turn our attention to the Aristotelian theory of law, which is to be found—even if merely sketched—in his Ethics and his Politics. For in the legal sphere, the "technical" necessity for positive rules as stable and institutionalised devices guiding the practice seems more evident. Aristotle's theory of law includes a fundamental thesis about the "rule of laws, not of men" which is indeed based upon the postulate of a system of general, positive rules conceived of as the essential instruments for the public organization of the polis. Aristotle thinks of these rules—actually, the rules of "legal justice" (nomikon dikaion)—as strictly universal (katholou), not merely empirical rules (or "rules of thumb"), their peculiar particularity and variability notwithstanding. It would be erroneous then, if only for this reason, to think (as it is, however, frequently done) that the Aristotelian system is completely unaware of the idea of a "natural law". For instance, Aquinas's definition of lex as regula et mensura is directly taken from the Nicomachean Ethics. Nevertheless, this Aristotelian "natural law" is about values and principles and no longer only about rules, and of course it is not "natural" at all in the sense of the natural law theories either. Rather these are principles of a moral-political kind, thus immanent to prāxis and hence to law as an "architectonic" institution