How we cite our quotes: (Book.Chapter.Bekker #s); all Bekker line numbers are approximate, since they are keyed to the original Greek.
Quote #4
And pain unhinges a person and destroys the nature of him who undergoes it, whereas pleasure does no such thing. (3.12.1119a24-25)
This simple observation on the nature of pain reveals something larger about human existence. Though living is, in itself, a great good, our ability to be virtuous and therefore happy is dependent on several factors. We can see here that when it comes to pain, all bets are off. It can erase our virtues and our intellect, and it can take away our power to make good choices. It's because of this transformative power that Aristotle says cowardice is more forgivable than other things, since it's our fear of pain that motivates it.
Quote #5
Metaphorically and in reference to a certain similarity, there is something just that pertains, not to a person in relation to himself, but to certain parts of himself...In these sorts of arguments, the part of the soul possessing reason is set apart from the nonrational; hence to those who look to these considerations, there does in fact seem to be injustice in relation to oneself, because in these parts of the soul, it is possible to suffer something contrary to their respective longings. (5.11.1138b6-13)
Aristotle's struggled with this question throughout Ethics up to this point: can we be unjust to ourselves?
His first answer says no: justice only exists for those who live in community, and according to laws.
But he wants to finesse this answer a bit more—perhaps to account for self-harming behaviors. In doing so, he gets very close to a psychology or inner life of a human being: we can be internally torn and we can rebel against our own better impulses and longings. In this way, we're a community unto ourselves, and reason is meant to be the ruler.
Quote #6
So let those things by which the soul attains the truth, by way of affirmation and denial, be five in number. These are art, science, prudence, wisdom, and intellect (for through conviction and opinion, one can be mistaken). (6.3.1139b15-18)
Aristotle tells us that it's through these five capacities that we perceive the world around us and make sense out of our observations. These are the intellectual virtues, and when guided by correct reason and the moral virtues, humans have a pretty good chance of getting at what's both good and pleasant in life.