An Aristotelian vocabulary:
"virtue" (arete) = excellence in fulfillment of a particular function
"happiness" (eudaimonia) = a sense of well-being, resulting from achieving excellence in the fulfillment of one's functions, including the "species-specific" functions of reason (both theoretical and practical)
Aristotle observes that each "science" ("knowledge," episteme) such as mathematics, ethics, politics, psychology, biology, physics, etc. admits of a given degree of certainty and demonstration. ("Knowledge comes in different flavors.") It is the mark of an educated human being - i.e., one who has explored the different sciences with some care - to know what degree of certainty and demonstration is appropriate to each one. In particular, the educated human being will know that the same degree of certainty and demonstration is not possible in ethics that is possible in mathematics.
There are important reasons for this claim - reasons surrounding the following passage. In speaking of the mean (between excess and defect) towards which our actions should aim, Aristotle notes:
...to what degree and how seriously a man must err to be blamed is not easy to define on principle. For in fact no object of perception is easy to define; and such questions of degree depend on particular circumstances, and the decision [krisis] lies with perception [aisthesis] (Nichomachean Ethics, II.ix.8)
Hold this together with a second passage:
...to experience these emotions [fear, courage, desire, anger, pity, and pleasure] at the right times and on the right occasions and toward the right persons and for the right causes and in the right manner is the mean or the supreme good, which is characteristic of virtue. (35 in Arthur)
And with a third passage:
By the mean considered relatively to ourselves I understand that which is neither too much nor too little; but this is not one thing, nor is it the same for everybody. Thus if 10 be too much and 2 too little we take 6 as a mean in respect of the thing itself; for 6 is as much greater than 2 as it is less than 10, and this is a mean in arithemtical proportion. But the mean considered relatively to ourselves must not be ascertained in this way. It does not follow that if 10 pounds ofmeat be too much and 2 be too little for a man to eat, a trainer will order him 6 pounds, as this may itself be too much or too little for the person who is to take it....the right amount will vary with the individual. This being so, everybody who understands his business avoids alike excess and deficiency; he seeks and chooses the mean, not the absolute mean, but the mean considered relatively to ourselves. (35 in Arthur)
Note the epistemological layers Aristotle is working through:
Object of knowledge
General/universal rule: "Virtue [excellence as a human being] then is a state of deliberate moral purpose consisting in a mean that is relative to ourselves, the mean being determined by reason...." (36 in Arthur)
Mode of Knowledge
Theoretical Reason /
Mathematical mean (arithemetical proportion)
|(theoretical reason - especially as calculative reason)|
|the ethical mean as relative to individuals||
Theoretical Reason /
in conjunction with...
|individual persons in particular circumstances, times, conditions, etc.||aisthesis (sense-perception)|
Aristotle thus argues for an epistemology which is unlike some claims about reason, feeling, and sense-perception which - using a dualistic, oppositional logic - require us to see an epistemological dualism:
|("Calculative") Reason over||
Passions / Feelings / Sense-perception
Passions / Feelings / Sense-perception
(romanticism, Star Wars?)
Rather, ethical and political knowledge for Aristotle is precisely not like pure mathematics, a knowledge (perhaps) sharply divorced from our sense-experience of the material domain. On the contrary, precisely because ethics and politics are practical sciences - i.e., having to do with how we "practice" with one another both privately (ethics) and communally (politics) - these sciences require aisthesis, the sense-perception that gives us information about the particulars to which our theoretical guidelines and rules are to apply.
Ethics and politics, in short, involve the constant interaction between theoretical/practical reason and the senses, in the effort to determine the appropriate mean(s) with regard to our emotions, etc.
Understanding this epistemology and vocabulary should then help you better understand other crucial passages:
"the good of man is activity of soul [psyche] in accordance with virtue [excellence], or, if there are more virtues than one, in accordance with the best and most complete virtue." (33 in Arthur)
[A "happy" man is] one who is active in accord with perfect virtue and adequately furnished with external goods, not for some chance period of time, but for his whole lifetime. (34 in Arthur - because achieving virtue requires a moderate amount of material foundation)
Our present study is not, like other studies, purely theoretical in intention; for the object of our inquiry is not to know what virtue is but how to become good, and that is the sole benefit of it. We must, therefore, consider the right way of performing actions, for it is acts that determine the character of the resulting moral states. (35 in Arthur, emphasis added)
The virtue or excellence of man will be such a moral state as makes a man good and able to perform his proper function well. (35 in Arthur)
Please notice, finally, that the mean as relative to ourselves - where the judgment/decision depends on sense-perception - stands as a "quasi-universal" or "relative absolute" - i.e., a universal which can be applied, interpreted, understood in different ways in different contexts, etc. (This is the sort of value/belief system I've associated with the "'constructivist'/intersubjectivity" and critical rationalism positions in the materials on "Reason, Revolution, Relativism, and Reactionaries" materials.)
Finally, consider the following from the last book in the Nichomachean Ethics:
In fact, however, arguments seem to have enough influence to stimulate and encourage the civilized ones among the young people, and perhaps to make virtue [excellence] take possession of a well-born character that truly loves what is fine; but they seem unable to stimulate the many towards being fine and good.
For the many naturally obey fear, not shame; they avoid what is base because of the penalties, not because it is disgraceful. For since they live by their feelings, they pursue their proper pleasures and the sources of them, and avoid the opposed pains, and have not even a notion of what is fine and truly pleasant, since they have had no taste of it.
What argument could reform people like these? For it is impossible, or not easy, to alter by argument what has long been absorbed by habit [_ethos_]....
Arguments and teaching surely do not influence everyone, but the soul of the student needs to have been prepared by habits for enjoying and hating finely, like ground that is to nourish seed. For someone whose life follows his feelings would not even listen to an argument turning him away, or comprehend it; and in that state how could he be persuaded to change? And in general feelings seem to yield to force, not to argument.
-- Aristotle, Nichomachean Ethics, Book X, section 9, emphasis added