4. Marcus: Let us, then, once more examine, before we come to the consideration of particular laws, what is the power and nature of law in general; lest, when we come to refer everything to it, we occasionally make mistakes from the employment of incorrect language, and show ourselves ignorant of the force of those terms which we ought to employ in the definition of laws.

Quintus: This is a very necessary caution, and the proper method of seeking truth.

Marcus: This, then, as it appears to me, has been the decision of the wisest philosophers — that law was neither a thing to be contrived by the genius of man, nor established by any decree of the people, but a certain eternal principle, which governs the entire universe, wisely commanding what is right and prohibiting what is wrong. Therefore, they called that aboriginal and supreme law the mind of God, enjoining or forbidding each separate thing in accordance with reason. On which account it is that this law, which the gods have bestowed upon the human race, is so justly applauded. For it is the reason and mind of a wise Being equally able to urge us to good or to deter us from evil.

Quintus: You have, on more than one occasion, already touched on this topic. But before you come to treat of the laws of nations, I wish you would endeavor to explain the force and power of this divine and celestial law, lest the torrent of custom should overwhelm our understanding, and betray us into the vulgar method of expression.

Marcus: From our childhood we have learned, my Quintus, to call such phrases as this "that a man appeals to justice, and goes to law," and many similar expressions "law," but, nevertheless, we should understand that these, and other similar commandments and prohibitions, have sufficient power to lead us on to virtuous actions and to call us away from vicious ones. Which power is not only far more ancient than any existence of states and people, but is coeval with God himself, who beholds and governs both heaven and earth. For it is impossible that the divine mind can exist in a state devoid of reason; and divine reason must necessarily be possessed of a power to determine what is virtuous and what is vicious. Nor, because it was nowhere written, that one man should maintain the pass of a bridge against the enemy's whole army, and that he should order the bridge behind him to be cut down, are we therefore to imagine that the valiant Cocles [i.e., Horatius] did not perform this great exploit agreeably to the laws of nature and the dictates of true bravery. Again, though in the reign of Tarquin there was no written law concerning adultery, it does not therefore follow that Sextus Tarquinius did not offend against the eternal law when he committed a rape on Lucretia, daughter of Tricipitius. For, even then he had the light of reason from the nature of things, that incites to good actions and dissuades from evil ones; and which does not begin for the first time to be a law when it is drawn up in writing, but from the first moment that it exists. And this existence of moral obligation is co-eternal with that of the divine mind. Therefore, the true and supreme law, whose commands and prohibitions are equally authoritative, is the right reason of the Sovereign Jupiter.