§ 19.
1. Parmenides, whom Aristotle (Met. 1, 5.) makes a pupil of Xenophanes, was born at Elea about B.C., 515, or 510, and was therefore a younger contemporary of Xenophanes. Following in the wake of this philosopher he formulated in its fulness the metaphysical principle of the Eleatic doctrine, and in such fashion that the Monistic theory in his hands attained a thoroughly idealistic development. He appears to have exercised an influence for good on the legislation and on the morals of his native city. Plato pays the highest tribute to his moral character as well as to his philosophy. His principal work was a didactic poem peri phuseôs, of which fragments have been preserved by Sextus Empiricus (adv. Math. 7, 111.), by Diogenes Laertius (9, 22) by Proclus (on the Timaeus of Plato), and by Simplicius (on Aristotle's Physics).
2. The speculative doctrines of Parmenides may be summed up in the following propositions: --
Being alone exists; Non-being is nothing. Hence there is no beginning of Being. How could that which exists begin to be? It could not come from the non-existent, for this is nothing; it could not come from the existent, for it is itself the existent.
Being is absolutely one; outside the unit of Being there is nothing, consequently the supposed plurality of things, and the changes of things dependent on this plurality are mere appearances.
Being is eternal and unchangeable, without birth or beginning, immutable, limited only by itself. In form it is a beautifully rounded sphere, one and eternal, the space within which is occupied without any vacuum.
Being is, furthermore, nothing else than the thought in which it is known. The thought itself is Being. Being and the concept of Being are one. In this sense all Being is pregnant with reason, and reason permeates all things.
Truth belongs entirely to thought. As Being alone is thinkable, so also that alone which is thinkable and thought is Being. The senses do not bring us truth. They only deceive us, and it is precisely this. deception of the senses which seduces men into the belief in, and the graceful tricks of speech about the multiplicity and the changes of things.
3. In his physical theories Parmenides endeavours to explain (hypothetically) that phenomenal world which the operations of thought show to be unreal. In this explanation he sets out from two opposing principles which bear to one another in the sphere of appearances the same relation that exists between Being and Non-being. These principles are Light and Night, with which the antithesis of Warm and Cold, Fire and Earth, is connected. On the proportions in which these principles or elements are mingled depend the plurality and differences of things in the world of phenomena. The force at work in these processes is Eros, the oldest of the gods. The soul is a mixture of the four elements.