Many of Parmenides's qualities were the direct opposite of Heraclitus. Heraclitus grasped his truths through intuition. He saw and knew the world of Becoming. Parmenides, however, arrived at his truths through pure logic. He calculated and deduced his doctrine of Being.
Parmenides had an early doctrine and a later, different, teaching. Nietzsche claimed that Parmenides's two ways of thinking not only divided his own life into two periods but also separated all pre-Socratic thinking into two halves. The earlier way was the Anaximandrean period. This dealt with two worlds: the world of Becoming and the world of Being. The second was the Parmenidean. In this world, there is no becoming, change, or impermanence. There is only Being.
The qualities of the world, Parmenides thought, were divided into opposites. There are positive qualities and there are their opposite negations. His division was based on abstract logic and not on the evidence of the senses. This dichotomy of positive and negative then became the separation into the existent and the nonexistent. For things to become, there must be an existent and a non-existent. Desire unites these opposites and creates the world of Becoming. When desire is satisfied, the existent and the nonexistent oppose each other and the things pass away.
Nietzsche did not think that an external event led to Parmenides's denial of Becoming. The influence of Xenophanes is made negligible by Nietzsche. Even though both men gave great importance to the concept of unity, Xenophanes communicated in ways that were alien to Parmenides. Xenophanes was a philosophical poet whose view of mystic unity was related to religion. He was an ethicist who rejected the contemporary values of Greece. Nietzsche claimed that the common attribute between Parmenides and Xenophanes was their love of personal freedom and unconventionality, not their emphasis on oneness.
The internal event that led to Parmenides's denial of Becoming began when he considered the nature of negative qualities. He asked himself whether something that has no being can have being. Logically, this was the same as asking whether A is not A. Parmenides then realized that what is, is. Also, what is not, is not. His previous thinking about negative qualities was then seen as being very illogical. Heraclitus's contradictory statements were considered to be totally irrational.
If that which is, is, and that which is not, is not, then several conclusions follow. That which truly is must be forever present. The existent also is not divisible, because there is no other existent to divide it. It is also immobile and finite. In sum, there is only eternal oneness.
The senses lead us to believe otherwise. Therefore, for Parmenides, the senses are illusive, mendacious, and deceitful. He accepted only his logical and rational conclusions. All sensual evidence was ignored. Parmenides only affirmed his extremely abstract, general truth which was totally unlike the reality of common experience.
Although logically certain, Parmenides's concept of being was empty of content. No sense perception illustrated this truth. "What is, is" is a judgement of pure thought, not experience. Nietzsche claimed that Parmenides created his concept of being from his own personal experience of feeling himself as alive. He then illogically attributed this general concept of absolute being to everything in the world. Thus, Nietzsche saw being as a subjective concept that was mistakenly asserted to be objective. Nietzsche's paraphrase of Parmenides's truth was, "I breathe, therefore being exists."
Along with his disciple Zeno of Elea, Parmenides stated that there is no such thing as infinity. If infinity exists, it would be the indivisible, immobile, eternal unity of being. In other words, it would be finite. Zeno's examples of flying arrows and Achilles chasing a tortoise show that motion over an infinite space would be impossible. But we do experience motion. The world does exhibit finite infinity. Parmenides rejects, then, the perceivable world of motion and asserts that reality agrees only with his logical concepts, which do not include finite infinity. For him, thinking and being are the same. What he thinks is what exists.
Objections can be raised against Parmenides's principles that sensual perception does not show true reality and that thinking is unmoving being. If the senses are unreal, how can they deceive? If thinking is immobile being, how does it move from concept to concept? Instead, it can be stated that the many things that are experienced by the senses are not deceptive. Also, motion can have being. No objection, however, can be made to Parmenides's self-evident main teaching that there is being, or, what is, is.