Another and kindred meaning of practical certitude in Vico is the so-called letter of the law, _formula legum;_ which may stand in opposition to reason and the moral consciousness, but none the less has its own peculiar value: "_dura lex, sed certa: durum sed scriptum est_--the law is harsh, but it is certain; it is harsh, but so it is written." It is in a word the value of law simply as law, which though devoid of any real ethical content yet has always the value that comes from a command over the will. "The certitude of law" (writes Vico) "is a darkening of the reason supported merely by authority, and makes the law harsh in practical experience by laying down their certitude, which in good Latin (_certuni_) means particularised, or in the scholastic terminology individualised." To a certain extent Vico grasped the individual character which lies at the root of every law. That one must "judge according to law, not according to example" (_legibus non exemplis iudicandum_) is a comparatively late principle: the first laws were strictly _"exempta,"_ exemplary punishments. From real examples were derived the ideal examples employed by logic and rhetoric: and when the intelligible universal was understood, it was recognised that law had a certain universal character.
The primitive society sketched by Vico is, in its juristic aspect, the myth so to speak of pure law or practical force. Once upon a time men lived possessed of immense bodily strength, and proportionately feeble in understanding, who thought all strength greater than their own divine, and this belief constituted their law. They thought of the gods simply as beings stronger than themselves, whom they were compelled to obey, though with a bad grace: like Polyphemus, who if he had been strong enough would have fought Zeus himself, or Achilles, who told Apollo that if only they were equally matched he would not hesitate to try his strength against him. The wisdom of providence decreed that these fierce men, not tamed as yet by the rule of reason, should at least fear the divine nature of force and measure reason by its standard. This is the foundation of the principle of the "external justice of war." But the myth of the period of force cannot have the strictness of a philosophical concept, and consequently these strong men are considered by Vico from another point of view as ethically the best: "strongest" and "best," _fortissimi_ and _optimi,_ are regarded as synonymous terms: and their law, though not truth or rational law, is not pure certitude, but truth "mixed with certitude," _ex certo mixtum._ But the very mixture of certitude with, and its preponderance over, truth, which is here asserted, postulates the concept of pure certitude as presupposed by Vico.