The aim of [Aristotle's Ethics] is the acquisition and propagation of a certain kind of knowledge (science), but this knowledge and the thinking which brings it about are subsidiary to a practical end. The knowledge aimed at is of what is best for man and of the conditions of its realisation. Such knowledge is that which in its consumate form we find in great statesmen, enabling them to organise and administer their states and regulate by law the life of the citizens to their advantage and happiness, but it is the same kind of knowledge which on a smaller scale secures success in the management of the family or of private life.
It is characteristic of such knowledge that it should be deficient in "exactness," in precision of statement, and closeness of logical concatenation. We must not look for a mathematics of conduct. The subject-matter of Human Conduct is not governed by necessary and uniform laws. But this does not mean that it is subject to no laws. There are general principles at work in it, and these can be formulated in "rules," which rules can be systematised or unified. It is all-important to remember that practical or moral rules are only general and always admit of exceptions, and that they arise not from the mere complexity of the facts, but from the liability of the facts to a certain unpredictable variation. At their very best, practical rules state probabilities, not certainties; a relative constancy of connection is all that exists, but it is enough to serve as a guide in life. Aristotle here holds the balance between a misleading hope of reducing the subject-matter of conduct to a few simple rigorous abstract principles, with conclusions necessarily issuing from them, and the view that it is the field of operation of inscrutable forces acting without predictable regularity. He does not pretend to find in it absolute uniformities, or to deduce the details from his principles. Hence, too, he insists on the necessity of experience as the source or test of all that he has to say. Moral experience—the actual possession and exercise of good character—is necessary truly to understand moral principles and profitably to apply them. The mere intellectual apprehension of them is not possible, or if possible, profitless.
[The first parts of the Ethics] lay down a principle which governs all Greek thought about human life, viz. that it is only intelligible when viewed as directed towards some end or good. This is the Greek way of expressing that all human life involves an ideal element—something which it is not yet and which under certain conditions it is to be. In that sense Greek Moral Philosophy is essentially idealistic. Further it is always assumed that all human practical activity is directed or "oriented" to a single end, and that that end is knowable or definable in advance of its realisation. To know it is not merely a matter of speculative interest, it is of the highest practical moment for only in the light of it can life be duly guided, and particularly only so can the state be properly organised and administered. This explains the stress laid throughout by Greek Moral Philosophy upon the necessity of knowledge as a condition of the best life. This knowledge is not, though it includes knowledge of the nature of man and his circumstances, it is knowledge of what is best—of man's supreme end or good.
But this end is not conceived as presented to him by a superior power nor even as something which ought to be. The presentation of the Moral Ideal as Duty is almost absent. From the outset it is identified with the object of desire, of what we not merely judge desirable but actually do desire, or that which would, if realised, satisfy human desire. In fact it is what we all, wise and simple, agree in naming "Happiness" (Welfare or Well-being).
In what then does happiness consist? Aristotle summarily sets aside the more or less popular identifications of it with abundance of physical pleasures, with political power and honour, with the mere possession of such superior gifts or attainments as normally entitle men to these, with wealth. None of these can constitute the end or good of man as such. On the other hand, he rejects his master Plato's conception of a good which is the end of the whole universe, or at least dismisses it as irrelevant to his present enquiry. The good towards which all human desires and practical activities are directed must be one conformable to man's special nature and circumstances and attainable by his efforts. There is in Aristotle's theory of human conduct no trace of Plato's "other worldliness", he brings the moral ideal in Bacon's phrase down to "right earth"—and so closer to the facts and problems of actual human living. Turning from criticism of others he states his own positive view of Happiness, and, though he avowedly states it merely in outline his account is pregnant with significance. Human Happiness lies in activity or energising, and that in a way peculiar to man with his given nature and his given circumstances, it is not theoretical, but practical: it is the activity not of reason but still of a being who possesses reason and applies it, and it presupposes in that being the development, and not merely the natural possession, of certain relevant powers and capacities. The last is the prime condition of successful living and therefore of satisfaction, but Aristotle does not ignore other conditions, such as length of life, wealth and good luck, the absence or diminution of which render happiness not impossible, but difficult of attainment.
Introduction to Aristotle's Ethics