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.
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.
As the pleasures of the body are the ones which we most often meet with, and as all men are capable of these, these have usurped the family title; and some men think these are the only pleasures that exist, because they are the only ones which they know.
All men naturally desire knowledge. An indication of this is our esteem for the senses; for apart from their use we esteem them for their own sake, and most of all the sense of sight. Not only with a view to action, but even when no action is contemplated, we prefer sight, generally speaking, to all the other senses. The reason of this is that of all the senses sight best helps us to know things, and reveals many distinctions.
Happiness is something final and complete in itself, as being the aim and end of all practical activities whatever .... Happiness then we define as the active exercise of the mind in conformity with perfect goodness or virtue.