§ 21.
1. Melissus, a native of the island of Samos, took an important part in the political concerns of his country. He was commander in a naval battle in which the Athenian fleet was defeated (B.C. 440). Simplicius has preserved several fragments of a work of Melissus peri tou ontos, or peri phusiôs. Its purpose is to establish the principle of Eleatic Monism by direct demonstration. "Oneness seems, however, to him to consist rather in the continuity of substance than in the notional unity of being."
2. Being exists, says Melissus, for if there were no being it would be impossible to speak of it. It cannot have become what it is, for it could only have arisen out of Non-being or out of Being. From Non-being nothing can arise, and it cannot have come from Being, for thus it would already have existed, and would not have arisen. Nor can Being perish; for it cannot become Non-being; and if it again become Being it has not ceased to be. Being is therefore eternal. From this we may deduce the following essential attributes of Being:--
Being is infinite. Since it is eternal it has neither beginning nor end. And what is without beginning or end is infinite. (Observe this transition from infinitude of time to infinitude of extension).
Being is one. If there were two existent beings the one would limit the other, and Being, it has been shown, is without end or limit.
Being is immovable and immutable. It is immovable, for motion supposes a vacuum, and vacuum there is none, since vacuum is Non-being and Non-being has no existence. it is immutable for (a.) change would involve plurality. Suppose for example, from rarefied it became dense, or from dense rarefied, the first would involve its becoming more, the second its becoming less. (b.) In case of change the actually existent should pass away, and, in part at least, become non-existent. If in the course of thirty thousand years this happened to the whole, the whole would in that time have passed away.
Being is furthermore indivisible. This follows from its unity and its immutability. Since it is indivisible it has no parts, and consequently is not a body -- a body without parts is unthinkable. It is, therefore, incorporeal.
3. What we see, hear and fed, is not true Being; otherwise it should have the attributes enumerated above. The multiplicity of things, motion and change are, therefore, appearances, not realities. In his physical theories Melissus does not differ materially from his predecessors of the same school.