out that both in his own day and later “in the times of Roman learning” he was spoken of in terms of the highest praise. In the variety of his knowledge, and in the importance of his influence on both Greek and modern speculation he was the Aristotle of the 5th century, while the sanity of his metaphysical theory has led many to regard him as the equal, if not the superior, of Plato.

His views may be treated under the following heads:—

1. The Atoms and Cosmology (adopted in part at least from the doctrines of Leucippus, though the relations between the two are hopelessly obscure). While agreeing with the Eleatics as to the eternal sameness of Being (nothing can arise out of nothing; nothing can be reduced to nothing), Democritus followed the physicists in denying its oneness and immobility. Movement and plurality being necessary to explain the phenomena of the universe and impossible without space (not-Being), he asserted that the latter had an equal right with Being to be considered existent. Being is the Full (πλῆρες, plenum); not-Being is the Void (κενόν, vacuum), the infinite space in which moved the infinite number of atoms into which the single Being of the Eleatics was broken up. These atoms are eternal and invisible; absolutely small, so small that their size cannot be diminished (hence the name ἄτομος, “indivisible”); absolutely full and incompressible, they are without pores and entirely fill the space they occupy; homogeneous, differing only in figure (as A from N), arrangement (as AN from NA), position (as N is Z on its side), magnitude (and consequently in weight, although some authorities dispute this). But while the atoms thus differ in quantity, their differences of quality are only apparent, due to the impressions caused on our senses by different configurations and combinations of atoms. A thing is only hot or cold, sweet or bitter, hard or soft by convention (νόμῳ); the only things that exist in reality (ἐτεῇ) are the atoms and the void. Locke’s distinction between primary and secondary qualities is here anticipated. Thus, the atoms of water and iron are the same, but those of the former, being smooth and round, and therefore unable to hook on to one another, roll over and over like small globes, whereas the atoms of iron, being rough, jagged and uneven, cling together and form a solid body. Since all phenomena are composed of the same eternal atoms (just as a tragedy and a comedy contain the same letters) it may be said that nothing comes into being or perishes in the absolute sense of the words (cf. the modern “indestructibility of matter” and “conservation of energy”), although the compounds of the atoms are liable to increase and decrease, appearance and disappearance—in other words, to birth and death. As the atoms are eternal and uncaused, so is motion; it has its origin in a preceding motion, and so on ad infinitum. For the Love and Hate of Empedocles and the Nous (Intelligence) of Anaxagoras, Democritus substituted fixed and necessary laws (not chance; that is a misrepresentation due chiefly to Cicero). Everything can be explained by a purely mechanical (but not fortuitous) system, in which there is no room for the idea of a providence or an intelligent cause working with a view to an end. The origin of the universe was explained as follows. An infinite number of atoms was carried downwards through infinite space. The larger (and heavier), falling with greater velocity, overtook and collided with the smaller (and lighter), which were thereby forced upwards. This caused various lateral and contrary movements, resulting in a whirling movement (δίνη) resembling the rotation of Anaxagoras, whereby similar atoms were brought together (as in the winnowing of grain) and united to form larger bodies and worlds. Atoms and void being infinite in number and extent, and motion having always existed, there must always have been an infinite number of worlds, all consisting of similar atoms, in various stages of growth and decay.

2. The Soul.—Democritus devoted considerable attention to the structure of the human body, the noblest portion of which he considered to be the soul, which everywhere pervades it, a psychic atom being intercalated between two corporeal atoms. Although, in accordance with his principles, Democritus was bound to regard the soul as material (composed of round, smooth, specially mobile atoms, identified with the fire-atoms floating in the air), he admitted a distinction between it and the body, and is even said to have looked upon it as something divine. These all-pervading soul atoms exercise different functions in different organs; the head is the seat of reason, the heart of anger, the liver of desire. Life is maintained by the inhalation of fresh atoms to replace those lost by exhalation, and when respiration, and consequently the supply of atoms, ceases, the result is death. It follows that the soul perishes with, and in the same sense as, the body.

3. Perception.—Sensations are the changes produced in the soul by external impressions, and are the result of contact, since every action of one body (and all representations are corporeal phenomena) upon another is of the nature of a shock. Certain emanations (ἀποῤῥοαί, ἀπόῤῥοιαι) or images (εἴδωλα), consisting of subtle atoms, thrown off from the surface of an object, penetrate the body through the pores. On the principle that like acts upon like, the particular senses are only affected by that which resembles them. We see by means of the eye alone, and hear by means of the ear alone, these organs being best adapted to receive the images or sound currents. The organs are thus merely conduits or passages through which the atoms pour into the soul. The eye, for example, is damp and porous, and the act of seeing consists in the reflection of the image (δείκελον) mirrored on the smooth moist surface of the pupil. To the interposition of air is due the fact that all visual images are to some extent blurred. At the same time Democritus distinguished between obscure (σκοτίη) cognition, resting on sensation alone, and genuine (γνησίη), which is the result of inquiry by reason, and is concerned with atoms and void, the only real existences. This knowledge, however, he confessed was exceedingly difficult to attain.

It is in Democritus first that we find a real attempt to explain colour. He regards black, red, white and green as primary. White is characteristically smooth, i.e. casting no shadow, even, flat; black is uneven, rough, shadowy and so on. The other colours result from various mixtures of these four, and are infinite in number. Colour itself is not objective; it is found not in the ultimate plenum and vacuum, but only in derived objects according to their physical qualities and relations.

4. Theology.—The system of Democritus was altogether anti-theistic. But, although he rejected the notion of a deity taking part in the creation or government of the universe, he yielded to popular prejudice so far as to admit the existence of a class of beings, of the same form as men, grander, composed of very subtle atoms, less liable to dissolution, but still mortal, dwelling in the upper regions of air. These beings also manifested themselves to man by means of images in dreams, communicated with him, and sometimes gave him an insight into the future. Some of them were benevolent, others malignant. According to Plutarch, Democritus