things for it was impossible, he conceived, that there should be a general common definition of any sensible object, since such were always in a state of change. The things, then, which were the subjects of universal truths he called Ideas; and held that objects of sense had their names according to Ideas and after them; so that things participated in that Idea which had the same name as was applied to them."

In agreement with this, we find the opinions suggested in the Parmenides of Plato, the dialogue which is considered by many to contain the most decided exposition of the doctrine of Ideas. In this dialogue, Parmenides is made to say to Socrates, then a young man, "O Socrates, philosophy has not yet claimed you for her own, as, in my judgment, she will claim you, and you will not dishonour her. As yet, like a young man as you are, you look But tell me this: it ap

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to the opinions of men. pears to you, as you say, that there are certain Kinds or Ideas (eidn) of which things partake and receive applications according to that of which they partake thus those things which partake of Likeness are called like; those things which partake of Greatness are called great; those things which partake of Beauty and Justice are called beautiful and just." To this Socrates assents. And in another part of the dialogue he shows that these Ideas are not included in our common knowledge, from whence

he infers that they are objects of the Divine mind.

26

In the Phædo the same opinion is maintained, and is summed up in this way, by a reporter of the last conversation of Socrates είναι τι ἕκαστον τῶν εἰδῶν, καὶ τούτων τ' άλλα μεταλαμβάνοντα αὐτῶν τούτων τὴν επωνυμίαν ἴσχειν; "that each Kind has an existence, and that other things partake of these Kinds, and are called according to the Kind of which they partake."

The inference drawn from this view was, that in order to obtain true and certain knowledge, men must elevate themselves, as much as possible, to these Ideas of the qualities which they have to consider: and as things were thus called after the Ideas, the Ideas had a priority and pre-eminence assigned them. The Idea of Good, Beautiful, and Wise, was the "First Good," the "First Beautiful," the "First Wise." This dignity and distinction were ultimately carried to a large extent. Those Ideas were described as eternal and self-subsisting, forming an "Intelligible World," full of the models or archetypes of created things. But it is not to our purpose here to consider the Platonic Ideas in their theological bearings. In physics they were applied in the same form as in morals. The primum calidum, primum frigidum, were those Ideas or fundamental Principles by participation of which, all things were hot or cold.

26 Phædo, p. 102.

This school did not much employ itself in the developement of its principles as applied to physical inquiries: but we are not without examples of such speculations. Plutarch's Treatise Пept Toù Пpúтov Yuxpoù, "On the First Cold," may be cited as one. Ψυχροῦ, It is in reality a discussion of a question which has been agitated in modern times also;—whether cold be a positive quality or a mere privation. "Is there, O Favorinus," he begins, "a First Power and Essence of the Cold, as Fire is of the Hot; by a certain presence and participation of which all other things are cold or is rather coldness a privation of heat, as darkness is of light, and rest of motion?"

3. Technical Forms of the Pythagoreans.-The Numbers of the Pythagoreans, when propounded as the explanation of physical phenomena, as they were, are still more obscure than the ideas of the Platonists. There were, indeed, considerable resemblances in the way in which these two kinds of notions were spoken of. Plato called his Ideas unities, monads; and as, according to him, Ideas, so, according to the Pythagoreans, Numbers, were the causes of things being what they are". But there was this difference, that things shared the nature of the Platonic Ideas "by participation," while they shared the nature of Pythagorean Numbers "by imitation." Moreover, the Pythagoreans followed their notion out into much greater developement than any other school, investing particular numbers 27 Arist. Metaph. i. 6.

with extraordinary attributes, and applying them by very strange and forced analogies. Thus the number Four, to which they gave the name of Tetractys, was held to be the most perfect number, and was conceived to correspond to the human soul, in some way which appears to be very imperfectly understood by the commentators of this philosophy.

It has been observed by a distinguished modern scholar, that the place which Pythagoras ascribed to his numbers is intelligible only by supposing that he confounded, first a numerical unit with a geometrical point, and then this with a material atom. But this criticism appears to place systems of physical philosophy under requisitions too severe. If all the essential properties and attributes of things were fully represented by the relations of number, the philosophy which supplied such an explanation of the universe, might well be excused from explaining also that existence of objects which is distinct from the existence of all their qualities and properties. The Pythagorean love of numerical speculations might have been combined with the doctrine of atoms, and the combination might have led to results well worth notice. But so far as we are aware, no such combination was attempted in the ancient schools of philosophy; and perhaps we of the present day are only just beginning to perceive, through the disclosures of chemistry and 28 Thirlwall's Hist. Gr. ii. 142.

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crystallography, the importance of such a line of inquiry.

4. Technical Forms of the Atomists and Others. -The atomic doctrine, of which we have just spoken, was one of the most definite of the physical doctrines of the ancients, and was applied with most perseverance and knowledge to the explanation of phenomena. Though, therefore, it led to no success of any consequence in ancient times, it served to transmit, through a long series of ages, a habit of really physical inquiry; and on this account, has been thought worthy of an historical disquisition by Bacon 29.

The technical term, Atom, marks sufficiently the nature of the opinion. According to this theory, the world consists of a collection of simple particles, of one kind of matter, and of indivisible smallness, (as the name indicates,) and by the various configurations and motions of these particles, all kinds of matter and all material phenomena are produced.

To this, the Atomic Doctrine of Leucippus and Democritus, was opposed the Homoiomeria of Anaxagoras; that is, the opinion that material things consist of particles which are homogeneous in each kind of body, but various in different kinds: thus for example, since by food the flesh and blood and bones of man increase, the author of this doctrine held that there are in food particles of flesh,

29 Parmenidis et Telesii et præcipue Democriti Philosophia, &c., Works, vol. ix. 317.