Jaeger saw Aristotle's departure from Athens in 347 as the expression of a crisis in his inner life and described that departure as a secession. Although we may readily believe that leaving Athens marked an important development in his relationship with the Academy, we know that he began to criticise the Platonists while still considering himself a member of their circle. He regularly uses the first person plural in referring to the Platonists in his critical review of their philosophy in Metaphysics A ch. 9, and even before that he had set out his objections to the theory of Forms at length in the lost work On Forms. His rejection of this central doctrine of Platonism may well date from a period when Plato was still alive. Ultimately Aristotle's criticisms of his master's theories extended over a very wide range of topics, including physics, cosmology, psychology and ethics. But the key to his reaction against the philosophy of Plato is undoubtedly his rejection of the theory of Forms. This was the corner-stone of his master's teaching and from the rejection of this doctrine many of his other minor objections stem.

Aristotle's arguments are directed not so much against the Plato we know from the Phaedo and the Republic, as against the Platonism current in the Academy in his own day. Indeed both the positions he attacked, and the arguments he used to attack them, owe a great deal to the discussions of the Academy.

This book is intended to help the student to discover and explore Aristotle. Most people would agree that he is not an easy philosopher to approach. His treatises cannot be read for enjoyment purely as literature, as many of Plato's dialogues can, and the man behind the treatises has the reputation of being a dry, uninspiring, even rather inhuman, person. If in the popular view Plato is as much a poet as a philosopher, Aristotle is still generally thought of first and foremost as a dogmatist and systematiser. This account of him, which is largely the product of a tendency to confuse Aristotle with Aristotelianism, is grossly exaggerated. Like Plato, he conceived the business of philosophy to consist as much in the defining of problems, the examining of alternative views, and the exploring of difficulties, as in the propounding of solutions, and his thought, like Plato's again, underwent a gradual evolution, even though this is, in his case, much more difficult to reconstruct owing to the nature of our evidence.

But while Aristotle is neither as unimaginative nor as inflexible as he is sometimes represented, no one can deny that his thought is often opaque. The treatises make slow and difficult reading, although their difficulty arises as much from the complexity and subtlety of their ideas as from the obscurity of Aristotle's expression. Yet however daunting the texts appear, there is no substitute for a close study of Aristotle's own words to grasp his philosophy.

The transmission of movement

The ultimate source of movement, in Aristotle's system, is the unmoved mover who acts as a final cause, by being loved. The ‘moved movers’—the heavenly bodies or more properly the spheres that carry them—transmit movement in turn as efficient causes. But whereas throughout the heavenly region movement is eternal and unchanging, in the region below the moon there is both movement and change. Change is brought about primarily because the course of the sun in the ecliptic is oblique to the axis of the earth. This oblique course of the sun causes the changes in the seasons, the ceaseless pendulumlike movement between the two extremes of the heat and dryness of summer and the cold and wet of winter, changes which are, of course, a good deal more striking in the Mediterranean than they are in our own more temperate climate.

In making the sun the source of change in the sublunary region Aristotle was no doubt chiefly influenced by the manifest fact that the generation and decay of many living things, especially plants, are closely linked with the seasons. There are, however, several serious difficulties both in his view of the relation between the heavenly and the sublunary regions, and in his theory of the transmission of movement from one to the other, and these must be considered before we discuss his account of the sublunary region as a whole.

Programme and methods

The last chapter of the Nicomachean Ethics points out that it is only by good legislation that society can ensure the good conduct of its citizens. The study of the behaviour of the individual is continuous with the study of society as a whole, and Aristotle mentions some of the main questions that need to be investigated under the second head. He complains that his predecessors had left the topic of legislation unexamined and he sketches out how he will deal with the subject. First he will review earlier ideas where they seem to have something to contribute to the subject. Then he will investigate, ‘in the light of the constitutions that have been collected’, what factors preserve or destroy constitutions and the reasons that some states are well, others badly, governed. Finally he will consider what constitution is best and what laws and customs the best state should have (EN 1181 b 12–23).

From the programme outlined here one might suppose that Aristotle undertook the detailed histories of individual constitutions, such as the Constitution of Athens, before writing the Politics, in which he deals with the causes of the changes in constitutions, the best possible form of state and so on. It might even appear that he followed, or claimed to be following, an idealistic work-plan, first completing the descriptive studies, and then and only then proceeding to the theoretical treatise.

Discussing the growth of Aristotle's thought, I argued that there is an important continuity in his development Naturally his views on many questions, including, for example, such a fundamental problem as the ultimate source of movement in the universe, changed during the course of his life, and he certainly also developed important, and engrossing, new interests. But whether any drastic revolution took place in his thought is doubtful.

Even his rejection of the teaching of Plato was not a matter of a simple, sudden and dramatic break so much as a complex, gradual and continuing process. His disagreements with his master date from early in his career and for some time after he had rejected the theory of Forms he still considered himself a member of the circle of Platonists. Conversely, long after his links with the Academy had become rather tenuous, there remained much in common between his mature philosophy and Plato's. Moreover while in zoology, for example, he pioneered a new approach to the study of the animal kingdom, his detailed investigations in that field tended to endorse certain doctrines, such as that of the final cause, that owe an obvious debt to Plato. Aristotle's work was wider-ranging and more original than that of any earlier philosopher, indeed of any philosopher of any time, but certain methodological assumptions and key ideas underlie a great deal of his thought.

Three separate ethical treatises are included in the Aristotelian Corpus, the Magna Moralia, the Eudemian Ethics and the Nicomachean Ethics. Of these the Magna Moralia is far from certainly authentic. Some scholars consider it an early work, composed while Aristotle was still much influenced by Plato, but it is more usually thought to have been written by one of Aristotle's pupils. Of the two other ethical treatises the Eudemian Ethics is generally held to be the earlier and it is useful both for the additional evidence it provides concerning some of Aristotle's ethical theories and more especially for the light it throws on their development. Our main source for his mature moral philosophy is, however, the Nicomachean Ethics, and it is with this that I shall be chiefly concerned in this chapter.

The plan of the ‘Nicomachean Ethics’

This is one of the most coherent and systematic of Aristotle's treatises and it is probably the easiest and most rewarding of all the major works for the student to tackle first. Unlike the Physics and the Metaphysics, which are collections of books that are often quite loosely connected to one another, the Nicomachean Ethics forms a coherent whole. Aristotle defines the subject and states the problem in book i. Books ii to v deal with moral virtue, first in general, then, after a discussion of choice and responsibility, in detail. Book vi deals with intellectual virtue, vii with moral weakness.