"We all suppose that the gods are alive and in work, since surely they are not asleep like Endymion [who, in myth, is said to have chosen eternal sleep so that his beauty would never fade]. And if someone is alive, and action is excluded, and production even more, nothing is left but contemplation (θεωρία). Hence the activity of the gods that is superior in blessedness is contemplation (τοῦ θεοῦ ἐνέργεια, μακαριότητι διαφέρουσα, θεωρητικὴ ἂν εἴη). The human activity most akin to this is the nature of happiness (εὐδαιμονίας). An indication is that other animals have no happiness, being completely deprived of contemplation. The whole life of the gods is blessed, and human life is blessed to the extent that it resembles this sort of activity, but none of the other animals is happy because none shares in contemplation at all. Happiness extends just so far as contemplation, and those to whom contemplation more fully belongs are more truly happy, not accidentally, but according to contemplation. Contemplation is valuable according to itself. Happiness, therefore, must be some form of contemplation (εὐδαιμονία θεωρία τις)" (Nicomachean Ethics X.8.1178b18-32).
(The Greek word θεωρία means generally something along the lines of "a looking at, viewing, or beholding." It transliterates as theoria and is the etymological root of the word theory. In philosophical contexts in Plato and Aristotle, it is traditionally translated as "contemplation." This practice derives from the use of the Latin contemplatio to translate θεωρία in Plato and Aristotle.)
Some Historical Background
The Timaeus provides some historical context for Aristotle's understanding of happiness and the best life for a human being.
The Timaeus is traditionally thought to be a late Platonic dialogue. The subject is the "universe" (κόσμος). Timaeus leads the discussion, not Socrates. Timaeus is said to have devoted himself to studying the nature of the universe. He explains the universe, beginning with its origin and ending with the existence of human beings (27a).
Timaeus explains that the universe is alive (30b), that it is a soul in a body, and that the bodily workings of the universe are the visible manifestation of what the universe thinks (34a, 36a). Happiness for a human being is a matter of transforming the reasoning part of the soul so that it is like the reason, or intelligence, in the cosmic soul. A human being must "redirect the revolutions" in his head. The "revolutions" in need of redirection are mistaken thoughts. To correct them, it is necessary to learn "the harmonies and revolutions of the universe." Since these "harmonies and revolutions" are what the cosmic soul thinks, a human being who acquires this theoretical understanding of things transforms himself so that his existence resembles the existence of the cosmic soul enjoys.
"The most sovereign (κυριωτάτου) part of our soul is god's gift to us, given to be our guiding spirit (δαίμονα). ... It raises us up away from the earth and toward what is akin to us in heaven, as though we are plants grown not from the earth but from heaven. ... And so if, the one hand, a man has become absorbed in his appetites (ἐπιθυμίας) or his ambitions and takes great pains to further them, all his opinions (δόγματα) are bound to become merely mortal. ... On the other hand, if a man has seriously devoted himself to the love of learning and to true wisdom (περὶ φιλομαθίαν καὶ περὶ τὰς ἀληθεῖς φρονήσεις), if has exercised these aspects of himself above all, then there is absolutely no way that his opinions can fail to be immortal and divine, should truth come within his grasp. And to the extent that human nature can partake of immortality, he can in no way fail to achieve this: constantly caring for his divine part as he does, keeping well-ordered the guiding spirit that lives within him, he must indeed be eminently happy (εὐδαίμονα). Now there is but one way to care for anything, and that is to provide for it the nourishment and the motions proper to it. And the motions that have an affinity to the divine part within us are the thoughts (διανοήσεις) and revolutions of the universe. These, surely, are the ones which each of us should follow. We should redirect the revolutions in our heads that were thrown off course at our birth, by coming to learn the harmonies and revolutions of the universe, and so bring into conformity with its objects our faculty of understanding, as it was in its original condition. And when this conformity is complete, we shall have achieved our goal; that most excellent life offered to humankind by the gods, both now and forevermore" (Timaeus 90a-d).
Aristotle transforms the picture from the Academy
Aristotle accepts in outline of the conception of human beings and their place in the universe that Timaeus describes, but Aristotle casts this conception within a new ontology.
Aristotle supposes that a human being becomes good and finds happiness by transforming his psychology so that he becomes like the unmovable first mover as much as possible. In part, this process happens according to nature. Induction, according to Aristotle, happens naturally and is for the acquisition of reason and the knowledge that belongs to reason, but human beings must perfect this cognition by acquiring expertise in theoretical science, most of all in the theoretical science of theology. The unmovable first mover is somehow fixed in a set of thoughts whose content is somehow the structure of existence, and a human being who transforms his psychology so that he has expertise in theology becomes as much like the unmovable first mover as human nature allows.
Reason in the Human Soul
Aristotle divides the part of the soul with reason divides into two parts. The first is the ἐπιστημονικὸν, the part capable or suited to ἐπιστήμη. The traditional translation of ἐπιστήμη in this context is 'knowledge,' but the English and the Greek here are not a perfect match. For Aristotle, "knowledge" (ἐπιστήμη) grasps relations of consequence and incompatibility among universals.
"Knowledge (ἐπιστήμη) is a demonstrative state (ἕξις ἀποδεικτική)" (Nicomachean Ethics VI.3.1139b).
"Knowledge (ἐπιστήμη) is a taking up (ὑπόληψις) about universals (καθόλου), things that are by necessity" (Nicomachean Ethics VI.6.1140b).
Knowledge is about universals
Aristotle's contrast between the medical practitioner and theorist helps show how he understands the cognition he identifies as "knowledge (ἐπιστήμη).
As a matter of "experience" (ἐμπειρία), the practitioner forms the generalization that patients who look a certain way respond to a certain treatment. This does not suffice for "knowledge" (ἐπιστήμη) because the practitioner does not grasp the universal feature that distinguishes those who benefit when they suffer from the disease from those who do not benefit. Aristotle cites having a phlegmatic condition is the example of such a feature. It is only by grasping such a feature that a human being can form more than the empirical generalization and thus have the knowledge in the judgment that all patients characterized by the feature will benefit from the treatment. The universal is part of the account of why the patients benefit. There is a necessary and hence universal connection between patients of the kind and benefiting from the treatment, and Aristotle thinks that this connection explains why the treatment is successful for patients with the disease.
"Whereas the other animals live by impressions and memories, and have but a ([comparatively] small share of experience, the human race lives also by art and reasoning (τέχνῃ καὶ λογισμοῖς). ... Experience seems very similar to science and art, but actually it is through experience that men acquire science and art (ἐπιστήμη καὶ τέχνη). ... Art is produced when from many notions of experience a single universal (καθόλου) judgment is formed with regard to like objects. To have a judgment that when Callias was suffering from this or that disease this or that benefited him, and similarly with Socrates and various other individuals, is a matter of experience; but to judge that it benefits all persons of a certain type, considered as a class, who suffer from this or that disease (e.g. the phlegmatic or bilious when suffering from burning fever) is a matter of art. ... We consider that knowledge and proficiency belong to art rather than to experience. .... Men of experience know that the thing is so, but do not know the why, while the others know the why and the cause (οἱ μὲν γὰρ ἔμπειροι τὸ ὅτι μὲν ἴσασι, διότι δ᾽ οὐκ ἴσασιν: οἱ δὲ τὸ διότι καὶ τὴν αἰτίαν γνωρίζουσιν)" (Metaphysics I.1.980b25-981a30).
Knowledge (ἐπιστήμη) and Intellect (νοῦς)
"Wisdom is intellect (νοῦς) plus knowledge (ἐπιστήμη)" (Nicomachean Ethics VI.7.1141a).
"Now of the thinking states by which we grasp truth, some are always true, others admit of error. Belief (δόξα) and reasoning (λογισμός) admit error, whereas knowledge (ἐπιστήμη) and intellect (νοῦς) are always true. No kind other than intellect is more precise than knowledge. Whereas starting-points of demonstrations are more cognizant (γνωριμώτεραι) and all knowledge involves an account (λόγου), there will not be knowledge of the starting-points, and since except intellect nothing can be truer than knowledge, it will be intellect that apprehends the starting-points" (Posterior Analytics II.19.100b).
Aristotle is part of an ancient philosophical tradition, going all the way back to Parmenides (middle of the 6th century BCE to middle of the 5th century BCE), in which there is a broad distinction between "reason" and "experience." This distinction first appears in an indeterminate form. Parmenides gives an example of "reason." He argues that nothing comes into or goes out of existence. In addition, Parmenides associates "experience" with perception broadly speaking. He does not set out the distinction any more precisely, but the way he champions "reason" over "experience" in connection with what exists was influential in the subsequent philosophical tradition. In this tradition, "reason" rather than "experience" is the correct form of cognition for understanding things. Later, under the influence of Socrates and Plato and also Aristotle, it became part of this tradition that "reason" is a form of cognition that that makes human beings into the distinctive kind of being they are.
Aristotle's discussion of the soul is part of this philosophical project to clarify "reason" and "experience." According to Aristotle, the cognition specific to the "intellect" (νοῦς) is "thinking" (νοεῖν). He conceives of "thinking" as a form of "discrimination" (κρίσις). The "intellect," according to Aristotle, grasps the universals that are the starting-points for demonstration.
"There are two things that most define the soul: movement in respect of place and thinking (νοεῖν), being sensible (φρονεῖν), and perceiving (αἰσθάνεσθαι). Thinking and being sensible are regarded as a kind of perception (for in both the soul discriminates (κρίνει) and is cognizant (γνωρίζει) of something). Indeed the ancients go so far as to say that being sensible and perceiving are the same. ... But it is apparent that being sensible and perceiving is not the same, for perception is present in all the animals but only some are sensible. Further, perceiving is distinct from thinking. In thinking we find right and wrong. We find right in being sensible, knowledge (ἐπιστήμη), true belief (δόξα ἀληθής), and we find wrong in their opposites. But perception of the special objects of the senses is always true, and is found in all animals, and while it is possible to think falsely, thinking is found only where there is reason (λόγος)" (On the Soul III.3.427a17-427b14).
Further, since Aristotle seems to hold that the "intellect" does not grasp the universals one by one in isolation, "thinking" does not take place without the advent of "knowledge" (ἐπιστήμη).
The Life of Contemplation (θεωρία) is the Best Life
Aristotle argues that happiness is not found in the pastimes by which we amuse ourselves. We amuse ourselves to relax, and we relax to prepare for the serious activity of living a good life (Nicomachean Ethics X.6.1176b). This is a life in accordance with certain virtues, and the life in which the best thing in a human being is in accordance with its proper virtue is the best life. Aristotle says that the best thing in a human being is "intellect" (νοῦς) and that the activity that expresses virtue of the "intellect" is "contemplation" (θεωρία).
Part of the argument is based on the premise (familiar from the similar argument in Plato's Republic) that what is proper to a thing is most pleasant for it.
"That which is proper (οἰκεῖον) to each thing is by nature (φύσει) the best and most pleasant for it. For man this the life according to the intellect (ὁ κατὰ τὸν νοῦν βίος), if this [the intellect] more than anything else is man (εἴπερ τοῦτο μάλιστα ἄνθρωπος). Therefore this life will be the happiest" (Nicomachean Ethics X.7.1178a).
Even given this premise, it is not clear that the conclusion follows. Aristotle thinks that "contemplation" (θεωρία) makes a substantial contribution to "happiness" (εὐδαιμονία). This much is clear, but Aristotle does not explain how this contribution is weighed in comparison with other things traditionally thought to contribute to or detract from happiness.