When we look at the matter from another point of view, great caution would seem to be required. For the habit of lightly changing the laws is an evil, and, when the advantage is small, some errors both of lawgivers and rulers had better be left; the citizen will not gain so much by making the change as he will lose by the habit of disobedience.
What we know is not capable of being otherwise; of things capable of being otherwise we do not know, when they have passed outsideour observation, whether they exist or not. Therefore the object of knowledge is of necessity. Therefore it is eternal; for things that are of necessity in the unqualified sense are all eternal; and things that are eternal are ungenerated and imperishable.
The saying of Protagoras is like the views we have mentioned; he said that man is the measure of all things, meaning simply that that which seems to each man assuredly is. If this is so, it follows that the same thing both is and is not, and is bad and good, and that the contents of all other opposite statements are true, because often a particular thing appears beautiful to some and ugly to others, and that which appears to each man is the measure
The first essential responsibility of the state is control of the market-place: there must be some official charged with the duty of seeing that honest dealing and good order prevail. For one of the well-nigh essential activities of all states is the buying and selling of goods to meet their mutual basic needs; this is the quickest way to self-sufficiency, which seems to be what moves men to combine under a single constitution.
There are three things that are the motives of choice and three that are the motives of avoidance; namely, the noble, the expedient, and the pleasant, and their opposites, the base, the harmful, and the painful. Now in respect of all these the good man is likely to go right and the bad to go wrong, but especially in respect of pleasure; for pleasure is common to man with the lower animals, and also it is a concomitant of all the objects of choice, since both the noble and the expedient appear to us pleasant.