(Ἀρχέλαος), a PHILOSOPHER of the Ionian school, called Physicus from having been the first to teach at Athens the physical doctrines of that philosophy. This statement, which is that of Laertius (2.16), is contradicted by the assertion of Clemens Alexandrinus (Strom. i. p. 30), that Anaxagoras μετήγαγεν ἀπὸ τῆς Ἰωνίας Ἀθήναζε τὴν διατριβήν, but the two may be reconciled by supposing with Clinton (F. H. ii. p. 51), that Archelaus was the first Athenian who did so. For the fact that he was a native of Athens, is considered by Ritter as nearly established on the authority of Simplicius (in Phys. Aristot. fol. 6, b.), as it was probably obtained by him from Theophrastus ; and we therefore reject the statement of other writers, that Archelaus was a Milesian. He was the son of Apollodorus, or as some say, of Mydon, Midon, (Suid.) or Myson, and is said to have taught at Lampsacus before he established himself at Athens. He is commonly reported to have numbered Socrates and Euripides among his pupils. If he was the instructor of the former, it is strange that he is never mentioned by Xenophon, Plato, or Aristotle; and the tradition which connects him with Euripides may have arisen from a confusion with his namesake Archelaus, king of Macedonia, the well-known patron of that poet.

The doctrine of Archelaus is remarkable, as forming a point of transition from the older to the newer form of philosophy in Greece. In the mental history of all nations it is observable that scientific inquiries are first confined to natural objects and afterwards pass into moral speculations; and so, among the Creks, the Ionians were occupied. with physics, the Socratic schools chiefly with ethics. Archelaus is the union of the two : he was the last recognized leader of the former (succeeding Diogenes of Apollonia in that character), and added to the physical system of his teacher, Anaxagoras, some attempts at moral speculation. He held that air and infinity (τὸ ἄπειρον) are the principle of all things, by which Plutarch (Plac. Phil. 1.3) supposes that he meant infinite air; and we are told, that by this statement he intended to exclude the operations of mind from the creation of the world. (Stob. Ecl. Phys. 1.1, 2.) If so, he abandoned the doctrine of Anaxagoras in its most important point; and it therefore seems safer to conclude with Ritter, that while he wished to inculcate the materialist notion that the mind is formed of air, he still held infinite mind to be the cause of all things. This explanation has the advantage of agreeing very fairly with that of Simplicius (l.c.) and as Anaxagoras himself did not accurately distinguish between mind and the animal soul, this confusion may have given rise to his pupil's doctrine. Archelaus deduced motion from the opposition of heat and cold, caused of course, if we adopt the above hypothesis, by the will of the material mind. This opposition separated fire and water, and produced a slimy mass of earth. While the earth was hardening, the action of heat upon its moisture gave birth to animals, which at first were nourished by the mud from which they sprang, and gradually acquired the power of propagating their species. All these animals were endowed with mind, but man separated from the others, and established laws and societies. It was just from this point of his physical theory that he seems to have passed into ethical speculation, by the proposition, that right and wrong are οὐ φύσει ἀλλὰ νόμῳ --a dogma probably suggested to him, in its form at least, by the contemporary Sophists. But when we consider the purely mechanical and materialistic character of his physics, which make every thing arise from the separation or distribution of the primary elements, we shall see that nothing, except the original chaotic mass, is strictly by nature (φύσει), and that Archelaus assigns the same origin to right and wrong that he does to man. Now a contemporaneous origin with that of the human race is not very different from what a sound system of philosophy would demand for these ideas, though of course such a system would maintain quite another origin of man; and therefore, assuming the Archelaic physical system, it does not necessarily follow, that his ethical principles are so destructive of all goodness as they appear. This view is made almost certain by thie tact that Democritus taught, that the ideas of sweet and bitter, warm and cold, &c., are )by νόμος, which can be accounted for only by a similar supposition.

Of the other doctrines of Archelaus we need only mention, that he asserted the earth to have the forin of an egg, the sun being the largest of the stars; and that he correctly accounted for speech by the motion of the air. For this, according to Plutarch (Plac. Phil. 4.19), he was indebted to Anaxagorans.

Archelaus flourished B. C. 450. In that year Anaxagoras withdrew from Athens, and during his absence Archelaus is said to have taught Socrates. (Laert. l.c.)