PERIPATETICS was the name given in antiquity to the followers of Aristotle, from their master's habit of walking up and down as he lectured conversationally to his pupils. Others derive the name from the repiraros, or covered walk of the Lyceum. An account of the Aristotelian philosophy will be found in the articles ARISTOTLE, ETHICS, LOGIC, and METAPHYSIC. Here it must suffice to recall those features of the system which mainly conditioned the development of the school. Aristotle's central conception is the correlative opposition of form and matter. This may be called the supreme category under which he views the world ; it is the point where, as Zeller puts it, Aristotle's system at once refutes and completes the Platonic doctrine of the " idea " in its relation to phenomena. But Aristotle did not succeed in expelling the dualism which he blamed in Plato. His deity is pure form, and dwells in abstract self-contemplation withdrawn from the actual life of the world. The development of the world remains, therefore, unrelated to the divine subject. In Aristotle's doctrine of man, precisely the same difficulty is experienced in connecting the active or passionless reason with the individual life, the latter being a process of development bound up with sense, imagination, and desire. The soul is originally defined as the entelechy of the body, and, moreover, not of body in general but of its particular body. It is impossible, therefore, from this point of view to speak of soul and body as separate entities. Yet Aristotle holds that besides the individual mind, which is all things potentially - which &mites all things - there is superinduced upon the process of development the active or creative reason, the pure actuality (114pyf ta) which the development presupposes as its necessary mills, just as the world-process presupposes God. This reason is "separable," and is said to enter "from without" when it unites itself to the process of individual life. It must therefore exist before the individual, and it alone outlasts the death of the body ; to it alone properly belong the titles of " immortal " and "divine." But its relation to the universal divine reason was not handled by Aristotle at all. The question was destined to become the erux of his commentators. In general it is evident that, if reason in man be identified with the process of natural development (and there is Aristotelian warrant for declaring these to be simply two aspects of the same thing), we drift into a purely naturalistic or materialistic doctrine. On the other hand, the doctrine of the "active reason " may be maintained, but what Aristotle left vague may be further defined. The rational soul of each individual may be explicitly identified with the divine reason. This leads to the denial of individual immortality and the doctrine of one immortal impersonal reason, such as we find, for example, in the rationalistic pantheism of Averroes. A third position is possible, if the statements of Aristotle be left in their original vagueness. Aristotle may then be interpreted as supporting monotheism and the immortality of separate rational souls. This was the reading adopted by the orthodox scholastic Aristotelians, as well as by those early Peripatetics who contented themselves with paraphrasing their master's doctrine.

Aristotle's immediate successors, Theophrastus, who presided over the Lyceum from 322 to 288 B.c., and Eudemus of Rhodes, were distinguished by a learned diligence rather than by original speculative power. They made no innovations upon the main doctrines of their master, and their industry is chiefly directed to supplementing his works in minor particulars. This they amplified the Aristotelian logic by the theory of the hypothetical and disjunctive syllogism, and added to the first figure of the categorical syllogism the five moods out of which the fourth figure was afterwards constructed. The impulse towards natural science and the systematizing of empirical details which distinguished Aristotle from Plato was shared by Theophrastus. His two works on the History of Plants and Causes of Plants prove him to have been a careful and acute observer. The same turn for detail is observable in his ethics, where, to judge from the imperfect evidence of the Characters, he elaborated still further Aristotle's portraiture of the virtues and their relative vices. In his doctrine of virtue the distinctive Peripatetic position regarding the importance of external goods was defended by him with emphasis against the assaults of the Stoics. He appears to have laid even more stress on this point than Aristotle himself, being doubtless led to do so, partly by the heat of controversy and partly by the importance which leisure and freedom from harassing cares naturally assumed to a man of his studious temperament. The metaphysical dr. optut of Theophrastus which have come down to us show that he was fully alive to the difficulties that start up round many of the Aristotelian definitions. But we are ignorant how he proposed to meet his own criticisms ; and they do not appear to have suggested to him an actual departure from his master's doctrine, much less any radical transformation of it. In the difficulties which he raises with reference to the relation of the active and the passive reason, as well as in his ascription of the physical predicate of motion to the activity of the soul, we may perhaps detect a leaning towards a naturalistic interpretation. The tendency of Eudemus, on the other hand, is more towards the theological or Platonic side of Aristotle's philosophy. The Eucreinian Ethics (which, with the possible exception of the three books common to this treatise and the Nicomachean Ethics, there need be no hesitation in ascribing to Eudemus) expressly identify Aristotle's ultimate ethical ideal of Oewpfa with the knowledge and contemplation of God. And this supplies Eudemus with a standard for the determination of the mean by reason, which Aristotle demanded, but himself left vague. Whatever furthers us in our progress towards a knowledge of God is good ; every hindrance is evil. The same spirit may be traced in the author of the chapters which appear as an appendix to book i. of Aristotle's Metaphysics. They have been attributed to Pasicles, the nephew of Eudemus. For the rest, Eudemus shows even less philosophical independence than Theophrastus. Among the Peripatetics of the first generation who had been personal disciples of Aristotle, time other chief names are those of Aristoxenus of Tarentum and Dicaearchus of Messene. Aristoxenus, "the musician," who had formerly belonged to the Pythagorean school, maintained the position, already combated by Plato in the Phxdo, that the soul is to be regarded as nothing more than the harmony of the body. Dicrearchus agreed with his friend in this naturalistic rendering of the Aristotelian entelechy, and is recorded to have argued formally against the immortality of the soul.

The naturalistic tendency of the school reached its full expression in Strato of Lampsacus, who succeeded Theophrastus as head of the Lyceum, and occupied that position for eighteen years (287-269 )Lc.). His predilection for natural science earned for him in antiquity the title of "the physicist." He is the most independent, and was probably the ablest, of the earlier Peripatetics. His system is based upon the formal denial of a transcendent deity. Cicero attributes to him the saying that he did not require the aid of the gods in the construction of the universe ; in other words, he reduced the formation of the world to the operation of natural forces. We have evidence that he did not substitute an immanent world-soul for Aristotle's extra-mundane deity; he recognized nothing beyond natural necessity. He was at issue, however, with the atomistic materialism of Democritus in regard to its twin assumptions of absolute atoms and infinite space. His own speculations led him rather to lay stress on the qualitative aspect of the world. The true explanation of things was to be found, according to Strato, in the forces which produced their attributes, and he followed Aristotle in deducing all phenomena from the fundamental attributes or elements of heat and cold. His psychological doctrine explained all the functions of the soul as modes of motion, and denied any separation of the reason from the faculties of sense-perception. He appealed in this connexion to the statement of Aristotle that we are unable to think without a sense-image.

The successors of Strato in the headship of the Lyceum were Lyco, Aristo of Ceos, Critolaus (who, with Carneadcs the Academic and Diogenes the Stoic, undertook in 155 nx. the famous embassy to Rome, more important in its philosophical than in its political bearings), Diodorus of Tyre, and Erynineus, who brings the philosophic succession down to about the year 100 B.C. Other Peripatetics belonging to this period are Hieronymus of Rhodes, Prytanis, and Phormio, the delirus senex who attempted to instruct Hannibal in the art of war. Sotion, Hermippus, and Satyrus were historians rather than philosophers. Heraclides Lembus, Agatharchides, and Antisthenes of Rhodes are names to us and nothing more. The philosophic unfruitfulness of the school during this whole period is expressly charged against it by Strabo, who explains it by his well-known story of the disappearance of Aristotle's writings after the death of Theophrastus. But it is impossible that this story should be true in the shape in which it is told by Strabo ; and a sufficient explanation of the barrenness of the school may be found in the general circumstances of the time. From the outset the characteristic of the Aristotelian philosophy had been its disinterested scientific character ; but the age was one for which speculation as such had lost its attractiveness. At such a time it was natural, therefore, that the Peripatetic school should suffer more than the others. It had also in practical matters taken up a mediatizing position, so that it lacked the attractions which, in the case of extreme views, enlist supporters -and inspire them with propagandist zeal. The fact, at all events, is not to be denied that, after Strato, the Peripatetic school has no thinker of any note to show for about 200 years. With Strato, moreover, the scientific activity of the school has an end ; when it received a new infusion of life its activity took another direction. Strato accuses the Peripatetics of this period of devoting themselves to the tricking out of commonplaces. This seems in great measure true of those who still occupied themselves with philosophy ; they cultivated ethics and rhetoric, and were noted for the elegance of their style. But the majority followed the current of the time, and gave themselves up to the historical, philological, and grammatical studies which mark the Alexandrian age.

Early in the 1st century B.c. all the philosophic schools began to be invaded by a spirit of eclecticism. This was partly the natural result of the decay of speculative interest and partly d-ue to the unconscious influence of Rome upon the philosophers. The Roman mind measured philosophy, like other things, by the standard of practical utility. As an instrument of education, and especially as the inculcator of moral principles, the Roman welcomed and appreciated philosophy ; but his general point of view was naively put by the proconsul Gellius (about 70 u.c.), who proposed to the representatives of the schools in Athens that they should settle their differences amicably, at the same time offering his personal services as mediator. Though the well-meant proposal was not accepted, this atmosphere of indifference imperceptibly influenced the attitude of the contending schools to one another. Thus Boethus the Stoic deserted the pantheism of his school and assigned the deity, as Aristotle had done, to the highest sphere. He likewise embraced the Peripatetic doctrine of the eternity of the world. A similar approximation to Peripateticism is seen in Panwtius. About the same time, Antiochus of Ascalon,founder of the so-called fifth Academy, tried to combine Plato, Aristotle, and Zeno, asserting that they differed only in words. Meanwhile the Peripatetic school may be said to have taken a new departure and a new lease of life. The impulse was due to Andronicus of Rhodes, the well-known editor of Aristotle's works, who presided over the Lyceum towards the middle of the 1st century B.C. His critical edition indicated to the later Peripatetics the direction in which they could profitably work, and the school devoted itself henceforth almost exclusively to the writing of commentaries on Aristotle. Boethus of Sidon and Aristo of Alexandria carried on the work of interpretation begun by Andronicus. Boethus appears, like many of his predecessors, to have taken the naturalistic view of Aristotle's doctrines, and even in some respects to have approximated to the Stoic materialism. Staseas, Cratippus, and Nicolaus of Damascus need only be named as belonging to this century. The most interesting Peripatetic work of the period is the treatise De Almelo, which has come down to us under Aristotle's name, but which internal evidence obliges us to assign to a date later than the writings of the Stoic Posidonius. The interest of the treatise lies in the evidence it affords within the Peripatetic school of the eclectic tendency which was then in the air. The admixture of Stoic elements is so great that some critics have attributed the work to a Stoic author ; but the writer's Peripateticism seems to be the more fundamental constituent of his doctrine.

Our knowledge of the Peripatetic school during the first two centuries of the Christian era is very fragmentary ; but those of its representatives of whom anything is known confined themselves entirely to commenting upon the different treatises of Aristotle. Thus Alexander of /Eke, the teacher of Nero, commented on the Categories and the De C. In the 2d century Aspasius and Adrastus wrote numerous commentaries. The latter also treated of the order of the Aristotelian writings in a separate work. Somewhat later, Herminus, Achaicus, and Sosigenes commented on the logical treatises. Aristocles of Messene, the teacher of Alexander of Aphrodisias, was the author of a complete critical history of Greek philosophy. This second phase of the activity of the school closes with the comprehensive labours of Alexander of Aphrodisias, the exegete par excellence, called sometimes the second Aristotle. He became head of the Lyceum during the reign of Septimius Severus, some time between 198 and 211 A.D. Alexander's interpretation proceeds throughout upon the naturalistic lines which have already become familiar to us. Aristotle had maintained that the individual alone is real, and had nevertheless asserted that the universal is the proper object of knowledge. Alexander seeks consistency by holding to the first position alone. The individual is prior to the universal, he says, not only "for us," hut also in itself, and universals are abstractions which have merely a subjective existence in the intelligence which abstracts them. Even the deity must be brought under the conception of individual substance. Such an interpretation enables us to understand how it was possible, at a later date, for Aristotle to be regarded as the father of Nominalism. Form, Alexander proceeds, is everywhere indivisible from matter. Hence the soul is inseparable from the body whose soul or form it is. Beason or intellect is bound up with the other faculties. It exists primarily in man only as a disposition or capacity-1;00s U)tL1 US Kai clmrtKtic - and is afterwards developed into actual intelligence - voi; 71-(ter-rp-os - the iutellectus acquisitus of the Scholastics. The active reason - voi33 7rocirtial5 - Which effects this development is, according to Alexander, no part of the soul, but simply the divine reason acting upon it. The influence of God upon nature is elsewhere reduced by Alexander, as far as possible, to a mechanical process. Aristotle's ethicomystical conception of God as the ultimate and transcendent object of desire is set aside ; and the influence of the deity is represented simply as a diffusion of force, first into the heavens and thence downwards, each lower element receiving less according to its greater distance from the source. The commentaries of the Aphrodisian formed the foundation of the Arabian and Scholastic study of Aristotle. Soon after Alexander's death the Peripatetic school was merged, like all others, in the Neoplatonic. Neoplatonists like Porphyry, Iamblichus, Themistius, Dexippus, Syrianus, Ammonius, Simplicius, and I'hiloponus carried on the work of commenting on Aristotle till the final disappearance of Greek philosophy. For the further history of Aristotelianism, see ARABIAN PHILOSOPHY and SCHOLASTICISM.

The authorities on whom we depend for our knowledge of the I'eripatetics are collected and sifted with exhaustive care by Zeller in the relative sections of his Philosophic dcr Griecheit (ii. 2 and iii. 1). (A. SE.)