Diogenes Laertius, Lives of the Philosophers

§ 10.147 If you reject absolutely any single sensation without stopping to discriminate with respect to that which awaits confirmation between matter of opinion and that which is already present, whether in sensation or in feelings or in any presentative perception of the mind, you will throw into confusion even the rest of your sensations by your groundless belief and so you will be rejecting the standard of truth altogether. If in your ideas based upon opinion you hastily affirm as true all that awaits confirmation as well as that which does not, you will not escape error, as you will be maintaining complete ambiguity whenever it is a case of judging between right and wrong opinion.

§ 10.148 If you do not on every separate occasion refer each of your actions to the end prescribed by nature, but instead of this in the act of choice or avoidance swerve aside to some other end, your acts will not be consistent with your theories. All such desires as lead to no pain when they remain ungratified are unnecessary, and the longing is easily got rid of, when the thing desired is difficult to procure or when the desires seem likely to produce harm. Of all the means which are procured by wisdom to ensure happiness throughout the whole of life, by far the most important is the acquisition of friends. The same conviction which inspires confidence that nothing we have to fear is eternal or even of long duration, also enables us to see that even in our limited conditions of life nothing enhances our security so much as friendship.

§ 10.149 Of our desires some are natural and necessary; others are natural, but not necessary; others, again, are neither natural nor necessary, but are due to illusory opinion. [ Epicurus regards as natural and necessary desires which bring relief from pain, as e.g. drink when we are thirsty; while by natural and not necessary he means those which merely diversify the pleasure without removing the pain, as e.g. costly viands; by the neither natural nor necessary he means desires for crowns and the erection of statues in one's honour. – Schol.] Those natural desires which entail no pain when not gratified, though their objects are vehemently pursued, are also due to illusory opinion; and when they are not got rid of, it is not because of their own nature, but because of the man's illusory opinion.

§ 10.150 Natural justice is a symbol or expression of expediency, to prevent one man from harming or being harmed by another. Those animals which are incapable of making covenants with one another, to the end that they may neither inflict nor suffer harm, are without either justice or injustice. And those tribes which either could not or would not form mutual covenants to the same end are in like case. There never was an absolute justice, but only an agreement made in reciprocal intercourse in whatever localities now and again from time to time, providing against the infliction or suffering of harm. [151]Injustice is not in itself an evil, but only in its consequence, viz. the terror which is excited by apprehension that those appointed to punish such offences will discover the injustice. It is impossible for the man who secretly violates any article of the social compact to feel confident that he will remain undiscovered, even if he has already escaped ten thousand times; for right on to the end of his life he is never sure he will not be detected. Taken generally, justice is the same for all, to wit, something found expedient in mutual intercourse; but in its application to particular cases of locality or conditions of whatever kind, it varies under different circumstances.

§ 10.152 Among the things accounted just by conventional law, whatever in the needs of mutual intercourse is attested to be expedient, is thereby stamped as just, whether or not it be the same for all; and in case any law is made and does not prove suitable to the expediencies of mutual intercourse, then this is no longer just. And should the expediency which is expressed by the law vary and only for a time correspond with the prior conception, nevertheless for the time being it was just, so long as we do not trouble ourselves about empty words, but look simply at the facts.

§ 10.153 Where without any change in circumstances the conventional laws, when judged by their consequences, were seen not to correspond with the notion of justice, such laws were not really just; but wherever the laws have ceased to be expedient in consequence of a change in circumstances, in that case the laws were for the time being just when they were expedient for the mutual intercourse of the citizens, and subsequently ceased to be just when they ceased to be expedient.

§ 10.154 He who best knew how to meet fear of external foes made into one family all the creatures he could; and those he could not, he at any rate did not treat as aliens; and where he found even this impossible, he avoided all intercourse, and, so far as was expedient, kept them at a distance. Those who were best able to provide themselves with the means of security against their neighbours, being thus in possession of the surest guarantee, passed the most agreeable life in each other's society; and their enjoyment of the fullest intimacy was such that, if one of them died before his time, the survivors did not lament his death as if it called for commiseration.