The knowledge of the soul admittedly contributes greatly to the advance of truth in general, and, above all, to our understanding of Nature, for the soul is in some sense the principle of animal life.
Again, it is possible to fail in many ways (for evil belongs to the class of the unlimited and good to that of the limited), while to succeed is possible only in one way (for which reason also one is easy and the other difficult—to miss the mark easy, to hit it difficult); for these reasons also, then, excess and defect are characteristic of vice, and the mean of virtue; For men are good in but one way, but bad in many.
Moral virtue is ... a mean between two vices, that of excess and that of defect, and ... it is no small task to hit the mean in each case, as it is not, for example, any chance comer, but only the geometer, who can find the center of a given circle.
The same things are best both for individuals and for states, and these are the things which the legislator ought to implant in the minds of his citizens.
It is clearly better that property should be private, but the use of it common; and the special business of the legislator is to create in men this benevolent disposition.
The government of freemen is nobler and implies more virtue than despotic government. Neither is a city to be deemed happy or a legislator to be praised because he trains his citizens to conquer and obtain dominion over their neighbors, for there is great evil in this.
Demonstration is also something necessary, because a demonstration cannot go otherwise than it does, ... And the cause of this lies with the primary premises/principles.
If we state the function of man to be a certain kind of life, and this to be an activity or actions of the soul implying a rational principle, and the function of a good man to be the good and noble performance of these, and if any action is well performed when it is performed in accordance with the appropriate excellence human good turns out to be activity of the soul in accordance with virtue, and if there are more than one virtue, in accordance with the best and most complete.
To the size of the state there is a limit, as there is to plants, animals and implements, for none of these retain their facility when they are too large.