At the first sight Heraclitus and Parmenides uphold the opposite principles, with their doctrines being in dramatic contrast, while the former affirms change, becoming and cyclic recurrence of things and the latter denies their existence. For Heraclitus true being is circular and transforms into not-being, life turns into death and the change that occurs is eternal and cyclical, it truly is (Graham). While for Parmenides true being is motionless and static, it does not change behind the appearance of change. Both philosophers indirectly abolished death by stamping becoming with the seal of being (McFarlane).
But, actually, Parmenides and Heraclitus asserted the One. They merely applied to different approaches to teach the same things. Heraclitus affirmed that diverse appearances change, therefore opposites exist in interconnection, depend on each other and are in unity. He conceived a unity of opposites and accepted becoming, while Parmenides refuted opposites, accentuated being and claimed: "Being is ungenerated and indestructible, whole, of one kind and unwavering and complete. Nor was it, nor will it be, since now it is, all together, one, continuous". Hereby, different appearances of reality do not truly change, because they so not exist. Parmenides considered that change is impossible, as everything is staying the same, being one single static element, but his opponent, Heraclitus, on the contrary, affirmed that everything is in constant flux, it is changing and his statement "everything flows" and "you cannot step into one and the same river twice" have become phrases. He argued that one cannot "step twice into the same river, nor touch mortal substance twice in the same condition. By the speed of change, it scatters, and gathers again", so the river will be different every time it is regarded (Graham). Claiming that motion is change, Heraclitus became known for his philosophy of universal "flux and fire" that, according to him, was the basic material of the world, as well as his controversial theory of coinciding opposites. The philosopher is considered to be independent of a definite school, as this heritage is multilayered and comprises elements of material monism and scientific cosmology, metaphysics and rationalism, but he definitely was a revolutionary whose works despite they were profoundly studied remain controversial and challenging to interpret (Graham).
The Greek philosopher presents uses the inductive method by means of which he wants the others to understand the world, he habitually presents a simple situation giving a concrete image, hereby he enables readers to educate themselves. To convey his beliefs more fruitfully Heraclitus uses such stylistic devices as chiasmus and alliteration in his speeches in defense of the theory. The philosopher diligently reiterates that his readers will not understand his message, but he promises to try to explain them everything he is able to see to: "distinguish each thing according to its nature and show how it is" (Graham). The form in which Heraclitus presents his work is essential for understanding its essence, he uses the technique of verbal complexity and syntactical ambiguity, Charles Kahn, for instance, characterizes his style with two words "linguistic density" and "resonance".
With his style similar to Hesoid and the Orphics Parmenides is supposed to have written only one work entitled "On Nature" that is unfortunately preserved only in fragments, though it originally extended to about eight hundred verses. Parmenides broke the prose tradition by writing it in hexameter verse and was widely quoted by the later authors who kept it for the future generations. The philosopher speaks in support of his principles in the Proem that has a number of interpretation variants and is regarded by contemporary scholars in the aspect of the strict monism, logical-dialectics, meta-principle etc. The work deals with the goddess who must reveal the two ways to Parmenides and he should chose the better one. The two ways present his former error and the truth that becomes clear to him. The work consists of two parts, the first one concerns the truth or "the true reality" and the second deals with the world of illusion, that is the world of senses and opinions. In the fragment 8 the goddess utters the philosopher's principle of the universal statics by claiming: "As yet a single tale of a way remains, that it is; and along this path markers are there very many, that What Is isâ€¦ whole and uniform, and still and perfect â€¦" with the past or the future being meaningless for the reason. Parmenides believed that "the reality is and must be in the strictest sense" and any alternation in it is not possible.
Remarkably, in Parmenides's Proem the goddess criticizes ordinary men for being guided with their senses. Unlike Heraclitus, the thinker judges merely by reason and never trusts the senses. In the human perception the world is nothing but a "deceitful show" (Palmer). Several other fragments found indicate that Parmenides touched upon the themes of physiology and human thought in his work and claimed that our own selves are deceptive and accentuated subjectivity of individual perception.
While Heraclitus also emphasizing human affairs is supposed to be the first humanist, who proves the blindness of humans in his doctrine. Though he believed that humans are frequently incapable of understanding, let alone wisdom, he does not deny the importance of senses and says: "The things of which there is sight, hearing, experience, I prefer". The philosopher connected accumulation of wisdom with senses and memory rather than with knowledge, and the latter does not necessarily teach humans understanding. So, in accordance with Heraclitus, people do not learn by experience, as they cannot process the information they perceive, however, humans still exercise "self-knowledge and sound thinking". To comprehend his insights one should catch their complexity and discover the unity of the elements (Graham).
According to Guthrie, for Parmenides there was no cosmology, as he presented the proofs of the impossibility of the opposites' existence. Conceiving the plurality of normal beliefs, the philosopher, however, makes mention of cosmology principles in the fragments 8 and 9 where he discusses light and night, as well as the stars, sun, moon and the earth itself. Commenting on his cosmology, Guthrie remarked that for he philosophy it remains just "a dialectical device" used for viewing the picture of the physical and sensible world (Palmer). The evidence of that is found in the goddess's words when she characterizes cosmology as: "the beliefs of mortals".
Contrary to Parmenides, Heraclitus being a cosmologist mentions in his texts the kosmos "order" describing the world around us, that he identifies with fire. Fire is described in his doctrine as the origin of all, all things are merely manifestations of fire and it is a symbol of change because it is never the same, without change, according to him, there will be no world. The elements are in cosmic balance and undergo the eternal transformations with no single element gaining predominance (Graham). Heraclitus says in his work: "The turnings of fire: first sea, and of sea half is earth, half fireburst". Unlike Parmenides, who proved the impossibility of the existence of opposites in his doctrine, Heraclitus entails the coincidence of opposites and discusses their interconnection, saying: "Sea is the purest and most polluted water: for fish drinkable and healthy, for men undrinkable and harmful". According to Herclitus, contrary qualities are included into "the same thing", he reasons that the same thing is living and dead at the same time, it is waking and sleeping, young and old (Graham). However, the philosopher accentuates that though the opposites are correlative, they are never identical to each other. But the coincidence of opposites results in contradictions that cannot be avoided by the philosopher. Barnes, for instance, blames the scholar for violating the principles of logic and making knowledge an impossible thing (Graham). Analyzing the philosopher's beliefs as those advocating the radical change, we see that Heraclitus' flux is a case of the unity of opposites described in his doctrine. But contemporary analysts claim, he cannot be both a believer in radical flux and a monist, so he is definitely a pluralist who urges self-control and moderation and regards the soul as the moral center of human existence (Graham). Despising passion, he admires the power received through self-mastery and self-purification: "It is not good for men to get all that they wish to get. Whatever our desire wishes to get, it purchases at the cost of soul".
Parmenides also discusses the behavior of the humans, is interested in the human thought and reasoning, though his discourse on that matter concerns cosmology. The interconnection becomes clearer as he discusses a wide range of natural phenomena. Being a rigid monist, Heraclitus believed in war, he even praised it calling it "a guiding force in the world" and claiming: "War is father of all and king of all; without the conflict we would have only lifeless uniformity". The philosopher as well as Parmenides speaks of God, however, Hercalitus means neither the Greek Gods nor a personal entity. He considers that God exists in every soul and in every single thing in the world. Due to his "fire and flux theory" he explains the presence of God in everything on earth. While Parmenides suggests that What Is is a god, and what must be "must be or exist and must be what it is, not only temporally but also spatially" (Palmer).
Though one thinks that the universe is static, eternal and motionless, denies change and becoming, another one affirms them and opens new perspectives for the Greek though by introducing his theory of "flux and fire", both have influenced the philosophic tradition and challenged the naÃ¯ve theories of their predecessors by developing more sophisticated ones. Parmenides, being a metaphysical monist, and Heraclitus, rather independent of any ancient theories, a material monist, a scientific cosmologist and a rationalist, have much more in common than it used to be generally recognized. Moreover, Heraclitus is supposed to inspire Parmenides for developing a contrasting theory, so that they could be seen as representatives advocating constant flux and universal stasis.