"You have often heard that the greatest thing to learn is the idea of good (τοῦ ἀγαθοῦ ἰδέα) by reference to which just things and all the rest become useful and beneficial" (Republic VI.505a).
"[T]hose who have survived the tests and approved themselves altogether the best in every task and form of knowledge must be brought at last to the goal. We shall require them to turn upwards the vision of their souls and fix their gaze on that which sheds light on all, and when they have thus beheld the good itself (τὸ ἀγαθὸν αὐτό) they shall use it as a pattern (παραδείγματι) for the right ordering of the state and the citizens and themselves throughout the remainder of their lives..." (Republic VII.539d-540a).
"Every art and every investigation, and likewise every action and choice, seems to aim at some good (ἀγαθοῦ). Hence the good is well describes as that which all things aim. ... Will not a knowledge of this good be of great importance for the conduct of life? Will it not better enable us to attain our end, like archers having a target to aim at? If so, we ought to make an attempt to determine at least in outline what the good is, and of which the sciences (ἐπιστημῶν) or capacities it is the object. Now this good seems to be the object of the most authoritative science, the one that, more than any other, is the ruling science. And the science of politics (ἡ πολιτικὴ) seems to be this science. For this science ordains which of the sciences are to exist in cities, and which ones each class in the city should learn, and how far. Again, we see that even the most highly esteemed of the capacities, such as generalship, household management, and oratory, are all subordinate to the science of politics. Further, it uses the other sciences concerned with action, and moreover lays down laws as to what people shall do and what things they shall refrain from doing" (Nicomachean Ethics I.1.1094a-b).
"Let us, then, begin again. Since all every sort of knowledge and choice is directed to the attainment of some good, what is the good which we say the aim of political science? That is, what is the highest of all the goods pursued in action? As far as the name goes, we may say that the great majority of mankind agree, since the multitude and persons of refinement say it is happiness (εὐδαιμονίαν), and suppose that living well and doing well are the same thing as being happy. What they disagree about is what happiness is" (Nicomachean Ethics I.1.1095a).
Two Perspectives on Ethics
Plato and Aristotle share what one might call a "teleological" perspective on ethics.
For Plato and Aristotle, very broadly speaking, the good is primary and defined independently of the right. The right is secondary. It is defined in terms the good and as what maximizes the good. An alternative to the teleological perspective on ethics is what one might call the "deontological" perspective. On this perspective on ethics, the the right is prior to the good. The deontological perspective has the important consequence that it allows for pluralism about the good. It frees individuals to pursue any life that make sense to them as long as this pursuit is permitted by the right, where the right consists in principles minimally necessary to give individuals the freedom to pursue lives that they themselves understand to be good lives.
Given these two perspectives on ethics, two questions arise. One is which perspective is correct. This is a philosophical question. It is the question of the appropriateness of a single determinate conception of the good life as a basis for formulating moral and political principles, given the existence of substantive diversity and conflict about how to live.
The other question is a historical question. It is the question why the teleological perspective seems so natural to Plato and Aristotle.
The Answer to the Historical Question
The answer to the historical question is difficult to know, but in part the answer seems to turn on the ancient idea that the explanation for regularity of behavior always involves intellect and intelligence. If something displays regularity in its behavior but is not itself intelligent, its behavior is thought to be a matter of design by an intellect.
Philosophers in the Presocratic Period tried to identify principles of reality and to explain whatever there is in terms of these principles. Plato and Aristotle thought that an explanation just in terms of material constituents was inadequate to explain the existence of objects and their behavior. They thought that an object behaves in its characteristic way because its constituents have a certain organization and order. Further, as part of the project of identifying the principles of reality, they thought that this order is somehow the result of an agent who determines and providentially governs reality.
Plato's "demiurge" (δημιουργὸς) is an example of this sort of principle (Timaeus 29a).
"[The δημιουργὸς] was good, and in him that is good no envy can arise. So, being without envy, he wished that all should be so far as possible like himself. This principle (ἀρχὴν) we shall be wholly right in accepting from men of wisdom as the supreme principle of becoming and the cosmos (κόσμου). Wishing, then, that as far as possible that all things should be good and nothing imperfect, the god (ὁ θεὸς) took over all that was visible, seeing that it was not in a state of rest but in a state of discordant and disorderly motion, He brought it into order out of disorder..." (Timaeus 29e-30a).
(Timaeus refers to demiurge as the "the maker and father of this universe (ποιητὴν καὶ πατέρα τοῦδε τοῦ παντὸς)" (Timaeus 28c), "the best of causes (ὁ δ᾽ ἄριστος τῶν αἰτίων)" (Timaeus 29a), and that the cosmos has "come to be through the providence of god (διὰ τὴν τοῦ θεοῦ γενέσθαι πρόνοιαν)" (Timaeus 30b).)
(The noun κόσμος transliterates as 'cosmos' and means "order." The corresponding verb κοσμέω (which 'cosmos' lacks) means "to order, arrange, rule." The cosmos is thus the order of the universe.)
Given this understanding of the order in things, it is possible to think that the orderly and regular behavior that characterizes human beings is somehow imposed by an intellect for an end. In the Timaeus, the demiurge "wished that all should be so far as possible like himself" (Timaeus 29a). This, then, determines which life above all others is best for a human being.
The Life of Contemplation (θεωρία)
The demiurge is an intellect. He imposed order on things according to a pattern "comprehensible by reason (λόγῳ) and thought" (Timaeus 29a).
It is part of this order that the demiurge imposes order so that the cosmos is a living thing and, like all living things, has a soul. The demiurge makes the world-soul and places it in the body of the world so that the whole rotates in a circle and is a blessed god (Timaeus 34b-36d). It is somehow part of the cosmos that the fixed stars, the earth, and the planets exist. The fixed stars are part of the outer sphere of the heaven, earth is at the center, and the planets in between (Timaeus 37c-40d). Further, it is part of the cosmos that human beings have their senses and in particular their sense of sight so that they can become like the world-soul. In this way, human beings also become like the demiurge since creates the cosmos to make things as much like him as possible.
"Let us conclude our discussion of the auxiliary causes that gave our eyes the power they now possess. We must next speak of that supremely beneficial function for which the god gave them to us. As my account has it, our sight has proved to be a source of supreme benefit to us, in that none of our present statements about the universe could ever have been made if we had never seen any stars, sun or heaven. The ability to see the periods of day-and-night, of months and of years, of equinoxes and solstices, has led to the invention of number, and has given us the idea of time and opened the path to inquiry into the nature of the universe. These pursuits have given us the love of wisdom (φιλοσοφίας), a gift from the god to the mortal race whose value neither has been nor ever will be surpassed. This is the supreme good our eyesight offers us. ... The god invented sight and gave it to us so that we might observe the orbits of intelligence in the universe and apply them to the revolutions of our own understanding. For there is a kinship between them, even though our revolutions are disturbed, whereas the universal orbits are undisturbed. So once we have come to know them and to share their ability to make correct calculations according to nature, we should stabilize the straying revolutions within ourselves by imitating the completely unstraying revolutions of the god" (Timaeus 46e-47c).
The Demiurge versus the Unmovable First Mover
Aristotle does not accept the demiurge, but his disagreement with Plato is not with the teleology. Aristotle argues that there can be no first or last moment of time, that time is a function of motion, and that the ultimate cause of this everlasting motion must itself be completely free from change. This understanding seems to rule out the craftsmanship model for teleology in nature.
"It is impossible that movement should come into being or cease to be; for it must always have existed. Nor can time come into being or cease to be; for there could not be a before or after if time did not exist. It follows that movement is continuous in the way time is; for time is the same thing as movement or an attribute of movement. And there is no continuous movement except movement in place, and of movement in place only that which is circular is continuous. ... If something acts, this will not be enough if its substance is potentiality; for there will not be eternal movement; for that which is potentially may possibly not be. There must be a starting point (ἀρχὴν) whose substance (οὐσία) is actuality (ἐνέργεια)" (Metaphysics XII.7.1071b). "There is, then, something which is always moved in an unceasing motion, which is motion in a circle; and this is plain not in theory only but in fact. The first heaven (πρῶτος οὐρανός) must be eternal, and there is something which moves it. And since that which is moved and moves is intermediate, there is a mover which moves without being moved, being eternal, substance, actuality (ἀΐδιον καὶ οὐσία καὶ ἐνέργεια)" (Metaphysics XII.7.1072a).
Aristotle seems to think that the sphere of fixed stars continuously and eternally moves in a circle around the earth and that all other motion and change depends on the motion of this outermost sphere in the universe. (The fixed stars appear to rise and set. The wandering stars are the planets, which seem to change their position relative to the fixed stars.) There are unmoved movers for each of the planetary spheres below the sphere of the fixed stars. These unmoved movers move without themselves moving. They are teleological causes of motion and change. There is an unmoved mover for sphere of the fixed stars, and this unmoved mover is one in number (Metaphysics XII.8.1074a). It is the unmovable first mover. The order in the world derives from it.
Further, just as sight in the Timaeus is for an end of becoming like the demiurge, Aristotle seems to think that human beings have some of their specific behavior (the behavior that belongs to individuals as members of a species) for the sake of becoming like the unmovable first mover. This behavior makes their existence like that of the unmovable first mover.
This is part of the idea in Aristotle's view that human beings acquire reason through the process of "induction" (ἐπαγωγή).
"All animals have an inborn discriminatory capacity, called perception. In some animals retention of the percept comes about, but in others it does not. ... When many such things come about, a difference comes about, so that some come to have reason (λόγον) from the retention of such things, and others do not. From perception there comes memory, and from memory (when it occurs often in connection with the same thing), experience (ἐμπειρία); for memories many in number from a single experience. From experience, or from the whole universal (καθόλου) that has come to rest in the soul (the one apart from the many, whatever is one and the same in all those things), there comes a starting-point of art (τέχνης) and of knowledge (ἐπιστήμης), of art if it deals with coming to be, of knowledge if it deals with being. Thus the states neither belong in us in a determinate form, nor come about from other more cognitive (γνωστικωτέρων) states; but they come about from perception—as in a battle when a rout occurs, if one man makes a stand another does and then another, until a position of strength is reached. The soul is such as to be capable of undergoing this" (Posterior Analytics II.99b-100a).
"All men naturally strive for knowledge (πάντες ἄνθρωποι τοῦ εἰδέναι ὀρέγονται φύσει)" (Metaphysics I.1.980a21).
The Deontological Perspective is the Minority Position
The deontological perspective is the minority position. It is only the Epicureans who do not believe in a god who governs the universe. They accept a contract theory of justice.
"Justice was never anything in itself, but a contract regularly arising at some place or other in people's dealings with one another, over not harming or being harmed" (Principal Beliefs 33; LS 22 A). "Taken generally, justice is the same for all, since it is something useful in people's social relationships. But in the light of what is peculiar to a region and to the whole range of determinants, the same thing does not turn out to be just for all. What is legally deemed to be just has its existence in the domain of justice whenever it is attested to be useful in the requirements of social relationships, whether or not it turns out to be the same for all. But if someone makes a law and it does not happen to accord with the utility of social relationships, it no longer has the nature of justice" (Principal Beliefs 36-37; LS 22 B).