Of all the questions which are ever the subject of discussion among learned men, there is none which is more important thoroughly to understand than this, that man is born for justice and that law and equity have  been established not by opinion but by nature.  This truth will become still more apparent if we investigate the nature of human association and society.

For there is not one thing so like or so equal to another, as in every instance man is to man... Therefore whatever definition we give of man will be applicable to the whole human race.  And this is a good argument that there is no dissimilarity of kind among men.  Because if this were the case, one definition could not include all men.

In fact, reason, which alone gives us so many advantage over beasts,...is assuredly common to all men; for the faculty of acquiring knowledge is similar in all human minds, though the knowledge itself may be endlessly diversified.  By the same sense we all perceive the same objects, and those things which move the sense at all, do move in the same way the senses of all men.  And those first crude elements of intelligence which, as I before observed, are the earliest developments of thought, are similarly impressed upon all men; and that faculty of speech which is the interpreter of the mind agrees in the ideas which it conveys, though it may differ in the words by which it expresses them.   And therefore there exists not a man in any nation, who, if he adopts nature for his guide, may not arrive at virtue.

Nor is this resemblance which all men bear to each other perceptible in those things only which are in accordance with the right reason, but also in errors, For all men alike are captivated by pleasure which, although it is a temptation to what is disgraceful, nevertheless bears some resemblance to natural good; for, as by its delicacy and sweetness it is delightful, it is through a mistake of the intellect adopted as something salutary....

It is therefore an absurd extravagance in some philosophers to assert that all things are necessarily just which are established by the civil laws and the institutions of nations.  Are then the laws of tyrants just, simply because they are laws?...  For there is but one essential justice which which cements society, and one law which establishes this justice.  This law is right reason, which is the true rule of all commandments and prohibitions. Whoever neglects this law, whether written or unwritten is necessarily unjust and wicked...

If nature does not ratify law, then all the virtues may lose their sway, for what becomes of generosity, patriotism and friendship?  Where will the desire of benefiting our neighbors, or the gratitude that acknowledges kindness, be able to exist at all?   For all these virtues proceed from our natural inclination to love mankind.   And this is the true basis of justice...

If the will of the people, the decrees of the senate, adjudications of magistrates, were sufficient to establish rights, then it might become right to rob, right to commit adultery, right to substitute forged wills, if such conduct were sanctioned by the votes or decrees of the multitude.  But if the opinions and suffrages of foolish men had sufficient weight to outbalance the nature of things, then why should they not determine among them that what is essentially bad and pernicious should henceforth pass for good and beneficial?  Or why, since law can make right out of injustice, should it not also be able to change evil into good?

But we have no other rule by which we may be capable of distinguishing between a good or a bad law than that of nature.  Nor is it only right and wrong which are discriminated by nature but generally all that is honorable is by this means distinguished from all that is shameful; for common sense has impressed in our minds the first principles of things and has given us a general acquaintance with them, by which we connect with virtue every honorable quality, and with vice all that is disgraceful.

SOURCE:  The Treatises of Cicero, tr., C. D. Yonge (London, 1853).  "On the Laws," Book I, chaps. 10-16.