Parmenides: 'What Is, Is; What Is Not, Is Not' — The Philosopher Who United Being and Thought

Key Takeaways

• "What is, is; what is not, is not": Parmenides placed the absolute distinction between Being (to eon) and non-Being at the foundation of philosophy. Non-Being can be neither thought nor spoken. From this principle, the impossibility of generation, destruction, change, and motion follows by strict logic. Western ontology begins here.
• The attributes of Being: ungenerated, imperishable, motionless, one, continuous: Being is neither born nor destroyed, neither divided nor moved. Like a perfect sphere, it is homogeneous, and exists neither in the past nor in the future but only in the "now." This rigorous deduction decisively shaped the method of all subsequent metaphysics.
• The Way of Truth and the Way of Opinion: The goddess presents two ways. One is the Way of Truth (Alētheia), which follows "what is, is." The other is the Way of Opinion (Doxa) of mortal beings, which follows the senses. The distinction between reason and the senses prepared the ground for Plato's theory of Forms.

Life and Historical Context

Parmenides was born around 515 BCE in the colonial city of Elea (modern Velia) in Magna Graecia (Greater Greece, southern Italy). Elea was a relatively young colony founded around 540 BCE by settlers from Phocaea who had fled the threat of Persia. According to Plato's dialogue Parmenides (127a–c), Parmenides visited Athens at about the age of sixty-five, accompanied by his pupil Zeno, and conversed with the young Socrates. The historicity of this meeting is debated, but the very fact that Plato staged it testifies to the immense importance he attached to Parmenides.

According to Diogenes Laërtius (Lives of the Eminent Philosophers IX.21–23), Parmenides came from a wealthy family and served as a lawgiver who gave Elea its laws. Plutarch likewise records that Parmenides brought good order to the city through excellent legislation (Against Colotes 1126A). That a philosopher was simultaneously a statesman is a characteristic trait shared by many ancient Greek thinkers.

In the 1960s, excavations at Porta Marina in Elea (modern Velia) uncovered an inscription dating to approximately the first century BCE. It reads: "Parmenides, son of Pyres, Ouliades, physikos (natural philosopher)." This inscription is physical evidence that Parmenides was honoured by later citizens of Elea as the city's intellectual hero. The title "Ouliades" suggests membership in a cultic association devoted to Apollo Oulios (Apollo the Healer), raising the possibility that Parmenides was also involved in medicine and religious cult. Philosopher, lawgiver, priest — this multifaceted portrait of Parmenides embodies the typical pre-Socratic intellectual.

His teachers are a matter of dispute. Diogenes Laërtius reports that he studied under Xenophanes (IX.21), but Aristotle is guarded about calling Parmenides Xenophanes' "pupil" (Metaphysics I.5, 986b22). Another tradition holds that he was influenced by a Pythagorean named Ameinias (Diogenes Laërtius IX.21). In any case, Parmenides' thought possesses an originality that far surpasses his predecessors.

The age in which he lived was the turbulent period of the Persian Wars (499–449 BCE). In the east, the Milesian school was asking about the origin of nature, and Heraclitus was proclaiming the flux of all things. In the west, the Pythagoreans were developing their philosophy of number and harmony. Parmenides would issue a challenge to all of these preceding currents of thought.

Mini-Timeline

• c. 540 BCE: Phocaean colonists found the city of Elea
• c. 515 BCE: Parmenides is born at Elea
• c. 500 BCE: Heraclitus' period of activity (at Ephesus)
• 499–494 BCE: The Ionian Revolt; fall of Miletus
• 490 BCE: The Battle of Marathon
• c. 480 BCE: Parmenides composes his didactic poem On Nature (Peri Physeōs) (estimated)
• 480 BCE: The Battle of Salamis
• c. 450 BCE: Parmenides visits Athens (according to Plato's Parmenides)
• c. 450 BCE: Death (estimated)

What Did This Philosopher Ask?

The philosophers before Parmenides asked "What is the origin (archē) of all things?" Thales proposed water, Anaximenes air, Heraclitus fire. Yet all of these inquiries remained within the framework of "what undergoes change" — none of them questioned the very possibility of change itself.

Parmenides' question was of an entirely different order. He asked not "what exists" but "what does 'to be' mean in the first place?" By rigorously pursuing the logical relationship between Being and non-Being, he brought change, generation, destruction, and plurality — all the basic features of the sensible world — before the judgement seat of logic.

This shift in questioning was decisive. Philosophy, which had relied on the observation of nature, now turned to inquiry grounded in pure logical reasoning. The discipline that Aristotle would later call "metaphysics" — the inquiry into Being as such — has its point of departure here. Plato called Parmenides a man "to be revered and feared" (Theaetetus 183e–184a) and made the struggle with Parmenides' philosophy a lifelong task.

Core Theories

1. "What Is, Is; What Is Not, Is Not" — The Logic of Being

The foundation of Parmenides' philosophy is the two ways set out in DK 28B2. The goddess declares to the young man:

"'The only ways of inquiry that can be thought of: the one, that it is, and that it is not possible for it not to be — this is the way of conviction (for it attends upon truth). The other, that it is not, and that it is necessary for it not to be — this, I tell you, is a path wholly without report.'" Source: DK 28B2 (quoted in Proclus, Commentary on the Timaeus I.345.18, and Simplicius, Commentary on the Physics 116.28)

The first way is "it is, and it cannot not be" — the Way of Being. The second is "it is not, and it must not be" — the Way of non-Being. The goddess immediately dismisses the second way, because "what is not" can be neither cognised nor expressed in language. "For thinking and being are the same" (DK 28B3) — whatever can be thought exists, and what does not exist cannot be thought.

This principle appears simple, but the consequences that follow from it are staggering. Change means that "what is" becomes "what is not," or that "what is not" becomes "what is." But "what is not" cannot exist. Therefore change is impossible. The senses report change, but reason refuses to accept it. This tension became the driving force of all philosophy after Parmenides.

To feel the force of this argument concretely, consider a thought experiment. Try to imagine a "round square." It is impossible — because the concept is self-contradictory, it cannot even become an object of thought. For Parmenides, "non-Being" is precisely this kind of impossibility. To think "what is not" is to posit "not being" as an object of thought — which is already to say that it "is." This self-contradiction is the engine of Parmenides' entire argument. When modern logicians debate the existential quantifier, at the bottom of their discussion lies the problem that Parmenides was the first to articulate clearly.

2. The Attributes of Being — Ungenerated, Imperishable, Motionless, One, Continuous

DK 28B8 is the longest surviving fragment of Parmenides' poem, and it deduces the attributes of Being with strict rigour. The goddess ascribes to Being the following characteristics: "ungenerated and imperishable, whole, of one kind, unshaken, and complete" (DK 28B8.3–4).

Ungenerated: Being is not born. If it were born, from what did it come? From non-Being? But non-Being "is not," so nothing can come from it. From Being? But what is already "is" — what would it mean for it to be born again? "What drove it to grow, starting from nothing, earlier or later?" (DK 28B8.6–7). The very assumption of a moment of generation is logically incoherent.

Imperishable: By the same logic, Being cannot perish. Perishing would mean "what is" becoming "what is not," but since "what is not" is impossible, Being cannot be destroyed.

Motionless and unchanging: For anything to move, it would need to move to a place where it currently is not — that is, to a void (non-Being). But a void is "what is not" and does not exist. Therefore motion is impossible. "It remains motionless in the bonds of mighty necessity" (DK 28B8.26).

One and continuous: For Being to be many, there would have to be something separating one being from another — non-Being. But non-Being is impossible. Therefore Being is undivided, continuous, and homogeneously one. "Being is not divisible, since it is all alike" (DK 28B8.22).

Temporal completeness: Being "neither was nor will be, but is now, all together, one, continuous" (DK 28B8.5–6). Past and future presuppose change, but change is impossible; therefore Being exists in an eternal present.

What guarantees all of these attributes is the power of "Necessity" (Anankē). Being is held "in the bonds of mighty Necessity" (DK 28B8.30–31). This necessity is not an external compulsion but the internal binding force of logic itself. From the premise "what is, is," each attribute of Being follows necessarily — and it is this deductive structure that makes Parmenides not a mere proclaimer but the first rigorous demonstrator in the history of Western philosophy. It is worth noting that "Necessity," "Justice" (Dikē), and "Fate" (Moira) are used almost synonymously in the poem. The fact that logical necessity is spoken of under the names of mythical powers is a characteristic duality running through the whole of Parmenides' poem.

At the close of fragment B8, the goddess describes Being as "like the mass of a well-rounded sphere (sphaira), equally poised from the centre in every direction" (DK 28B8.43–44). Whether this means a physical sphere or is a metaphor for completeness is debated, but the mainstream interpretation reads it as a figure for homogeneity and self-completeness.

3. The Revelation of the Goddess — Poetic Form and Philosophical Method

Parmenides' work is written not in prose but in the same hexameter verse as Homer and Hesiod. In DK 28B1 (the proem, prooimion), a young man rides in a chariot guided by the daughters of the Sun (Heliades), passes through the gates of Night and Day, and arrives before an unnamed goddess. This journey is not mere literary ornament. The chariot's axle "screams like a pipe" in the sockets of the wheels (B1.7), and the goddess Dikē (Justice) stands as gatekeeper at the mighty gate that separates Night from Day, holding its keys (B1.14). The Heliades persuade Dikē and the gate opens — a scene that symbolically conveys that the attainment of truth requires both logical inquiry (the guidance of the Heliades) and justice and order (the permission of Dikē).

The goddess tells the young man: "You must learn all things — both the unshaken heart of well-rounded Truth (Alētheia), and the opinions (doxai) of mortals, in which there is no true conviction" (DK 28B1.28–30).

Why did Parmenides write philosophical argument in verse? In part, he stood within the tradition of didactic poetry — Xenophanes and others before him also philosophised in verse. But more importantly, the framework of divine revelation signals the superhuman authority of truth. The truth Parmenides articulates is not a personal opinion; it is the necessary conclusion that logic itself compels — and this authority is underwritten by the form of divine revelation.

4. The Three Ways — Truth, Opinion, and the Third Way

In addition to the two ways set out in DK 28B2, DK 28B6 rejects a third way. This is the way that holds "that Being and non-Being are the same and not the same" — the habitual way of "mortals" who confuse Being with non-Being (DK 28B6.4–9).

Whom this third way targets is a matter of scholarly dispute. Some researchers see it as a criticism aimed at Heraclitus — for Heraclitus' claim that opposites are "the same" is precisely what blurs the distinction between Being and non-Being. Another interpretation holds that it is a critique of the ordinary human worldview — the unreflective acceptance of change and plurality.

In either case, the goddess demands a strict either/or. "Keep your thought far from this way of inquiry. Do not let habit born of experience force you along this way — to use an aimless eye, an echoing ear, and a tongue. But judge by reason (logos) the much-contested proof (elenchos) that I have spoken" (DK 28B7.3–6). Judge by reason, not by the senses — this demand is the prototype of Western rationalism.

5. The Way of Opinion — Why Did Parmenides Speak of the Phenomenal World?

The second half of the poem — the "Way of Opinion" (Doxa) — stands in sharp contrast to the Way of Truth, and develops a cosmology that explains the plurality of the sensible world. The goddess posits two "forms" — "Light" (fire) and "Night" (darkness) — as cosmological principles (DK 28B8.53–61, DK 28B9).

But why did Parmenides, who had denied change in the Way of Truth, go on to offer an account of the phenomenal world in the Way of Opinion? This has been one of the greatest interpretive puzzles since antiquity. The leading interpretations are as follows. (1) By presenting the best possible cosmology of mortals, the goddess shows that, even as an account of the sensible world, her explanation is second to none (the goddess herself says so at DK 28B8.60–61). (2) The cosmology serves as a negative lesson, revealing the structural defect inherent in any account of the sensible world. (3) It reflects the practical recognition that one cannot entirely ignore the sensible world in the conduct of life.

Although the surviving fragments of the Way of Opinion are few, the cosmology they sketch has an interest all its own. The goddess explains all things by the mixture of two forms — Light (fire) and Night (darkness). At the centre of the cosmos stands a daimōn (divinity) who governs all generation and mixture (DK 28B12). The heavens are composed of concentric rings (stephanai): the outermost ring is fire, the innermost is Night (testimony of Aëtius). Also noteworthy is the fragment on the determination of sex in embryos (DK 28B17), which proposes that the right side corresponds to male and the left to female. These fragments show that Parmenides was also conversant with the natural science of his day, and they confirm that the Way of Opinion was no mere negative appendix.

The very existence of the Way of Opinion shows that Parmenides was no simple dogmatist. How to resolve the tension between truth and appearance — this problem became a fundamental one, extending through Plato's theory of Forms, Aristotle's form-matter distinction, and even Kant's distinction between phenomena and things-in-themselves.

6. The Confrontation with Heraclitus — Change vs. Immutability

Heraclitus proclaimed the flux of all things and held that change is the fundamental character of reality. Parmenides took the diametrically opposite position. Change is logically impossible; the change reported by the senses is merely opinion (Doxa).

This confrontation split ancient philosophy in two. Do we accept change or accept immutability? Subsequent philosophers struggled between these two poles. Empedocles proposed the combination and separation of four elements; Anaxagoras posited infinitely many seeds (spermata); Democritus invoked atoms and the void — each attempting to explain change while circumventing Parmenides' logical constraints. Plato drew a line between an immutable realm of Forms and the changing sensible world, seeking to synthesise both positions. Aristotle distinguished potentiality (dynamis) from actuality (energeia) in order to show that change is not generation from non-Being.

The history of Western metaphysics is, in a sense, the history of responses to the problem Parmenides posed.

7. Zeno's Paradoxes — In Defence of the Master

Parmenides' pupil Zeno of Elea devised a series of paradoxes to defend his master's doctrines. Their purpose was to show that accepting plurality and motion leads to contradictions — a strategy known as reductio ad absurdum.

"Achilles and the Tortoise": The swift Achilles can never overtake the tortoise. By the time Achilles reaches the point where the tortoise was, the tortoise has moved farther ahead, and this process repeats ad infinitum. "The Flying Arrow Is at Rest": At each instant the arrow occupies a definite position, and what occupies a definite position is at rest. Therefore the flying arrow is not in motion (Aristotle, Physics VI.9, 239b30–33).

There is also the Dichotomy paradox: to traverse any distance, one must first traverse half of it; to traverse that half, one must first traverse half of that — and so on without end. Since one cannot traverse infinitely many intervals in finite time, motion cannot even begin. A rigorous resolution of this paradox came only with nineteenth-century mathematics. The precise definition of the limit concept by Cauchy and Weierstrass proved that the infinite series 1/2 + 1/4 + 1/8 + … = 1 converges to a finite value. The mathematical fact that infinitely many terms can sum to a finite value refutes Zeno's premise — that traversing infinitely many intervals requires infinite time. Yet whether this mathematical resolution fully dissolves the philosophical problem remains debatable. The relationship between the continuous and the discrete, the infinite and the finite, continues to be a central issue in the philosophy of mathematics today.

These paradoxes are not mere intellectual games. They raise fundamental questions about the relationship between continuity, infinite division, and motion — questions that had to wait for the nineteenth-century development of the concept of the limit for a rigorous mathematical treatment. Aristotle called Zeno "the inventor of dialectic" (Aristotle's testimony via Diogenes Laërtius IX.25).

Guide to Key Texts

• Parmenides, On Nature (Peri Physeōs) — His sole work: a didactic poem in hexameter verse. It consists of three parts: the Proem (prooimion), the Way of Truth (Alētheia), and the Way of Opinion (Doxa). Transmitted as fragments in DK 28B.
• Diels, H. & Kranz, W. Die Fragmente der Vorsokratiker (DK) — Parmenides is number 28. The fundamental reference for fragment studies.
• Gallop, David. Parmenides of Elea: Fragments (1984) — Greek text, English translation, and commentary. A standard introduction.
• Coxon, A.H. The Fragments of Parmenides (1986; rev. ed. 2009) — Detailed critical text and commentary. The definitive scholarly edition.
• Plato, Parmenides — A dialogue between Parmenides and the young Socrates. An advanced exercise in dialectic centred on the problem of the One and the Many.
• Plato, Sophist — Plato's attempt to overcome Parmenides' principle that "non-Being cannot be spoken" (the metaphor of "patricide").

Major Criticisms and Controversies

1. Plato's "patricide": In the Sophist (241d), Plato argued for the necessity of overcoming Parmenides' denial of non-Being. For falsehood and error to exist, it must be possible in some sense to say that "what is not" in some way "is." Plato called this a "patricide against Father Parmenides" and sought a resolution by redefining "is not" as "is different from" (heteron). Non-Being is not absolute "nothingness" but "that which is other" than a given thing — a turning point that proved decisive for the history of Western ontology.

2. Aristotle's critique: In Physics Book I, Aristotle subjected Parmenides' logic to detailed examination. The core of his criticism is that "is" is said in many ways. Parmenides treated "is" univocally, but in reality "is" is predicated across many categories — substance, quality, quantity, place, and so on (Metaphysics I.5, 986b22–987a2). Change is not generation from nothing but a transition from potentiality to actuality — an answer that took Parmenides' logic head-on and sought to transcend it.

3. The response of the Atomists: Leucippus and Democritus positively introduced the void (kenon) that Parmenides had denied. Each atom is itself Parmenidean "Being" — ungenerated, imperishable, unchanging — but atoms move through the void and combine and separate, thereby producing change. This was an ingenious response that partially accepted Parmenides' principles while granting a kind of reality to "non-Being" (the void).

4. Modern interpretive controversies: In contemporary scholarship, fierce debate continues over the interpretation of Parmenides' "is" (estin). Three positions compete: the existential reading ("exists"), the predicative reading ("is [such-and-such]"), and the veridical reading ("is true"). Each significantly alters the meaning of Parmenides' argument. The work of Owen (1960), Mourelatos (1970), and Curd (1998) has driven this debate.

5. Gorgias' On Non-Being: The sophist Gorgias, in his work On Non-Being, or On Nature (Peri tou mē ontos), parodied Parmenides' method by "demonstrating" three propositions: (1) nothing exists; (2) even if something exists, it cannot be known; (3) even if it can be known, it cannot be communicated to others. This turned Parmenides' "what is, is" on its head, using the same logical structure to derive the opposite conclusion. Whether Gorgias' intent was genuine philosophical refutation or a display of rhetorical virtuosity is debated, but the work is significant in that it paradoxically demonstrated the formal power of Parmenides' reasoning — change the premises, and the conclusion reverses.

Influence and Legacy

The Eleatic School: Parmenides is regarded as the founder of the Eleatic school. His pupil Zeno defended the master's thought with paradoxes of motion and plurality; Melissus of Samos extended the discussion by arguing that Being is infinite.

Plato: Plato's philosophy is unthinkable without Parmenides. The immutable realm of Forms is a philosophical development of Parmenidean "Being," and the sensible world corresponds to the domain of opinion. Parmenides, Sophist, Theaetetus — his major late dialogues are, each and all, a dialogue with Parmenides.

Aristotle: Aristotle's metaphysics — the multivocity of Being, the distinction between potentiality and actuality, the doctrine of the categories — was built as a response to the problems Parmenides raised.

The medieval and early modern periods: Parmenides' influence penetrated medieval theology via Neoplatonism. The tradition of onto-theology (Ontotheologie), which conceives of God as the supreme "Being," can be traced back to Parmenides.

Heidegger: Heidegger re-read Parmenides as the "beginning" (Anfang) of Western metaphysics. In his 1942–43 lecture course Parmenides (GA 54), he interpreted Alētheia (truth) as "unconcealment" and discerned in it a double movement of disclosure and concealment of Being. For Heidegger, Parmenides was the thinker who first — and most radically — thought the "question of Being" that the West had forgotten.

Early modern rationalism: Parmenides' principle that "what can be thought exists" reverberates through early modern rationalism. Descartes' "I think, therefore I am" rediscovers the inseparability of thought and being in individual consciousness. Spinoza's single substance (God-or-Nature) in the Ethics can be read as a modern variation on Parmenides' One. Leibniz's question "Why is there something rather than nothing?" likewise belongs to the problem-space of Being and nothingness that Parmenides opened up. The rationalist tradition — the attempt to disclose the structure of reality by pure reason alone — has its headwaters in Parmenides.

Connections to the Present

First, the relationship between logic and reality. Parmenides held that what is logically impossible is also impossible in reality. Modal logic in contemporary analytic philosophy — the logic of "possible," "necessary," and "impossible" — is a refinement of the conceptual apparatus that Parmenides was the first to deploy explicitly. Does logic reflect the structure of the world, or does it merely mark the limits of human thought? This question remains open.

Second, the problem of Being and nothingness. Modern physical cosmology confronts the question "Why is there something rather than nothing?" The vacuum of quantum mechanics is not absolute "nothing" but teems with quantum fluctuations. The principle Parmenides articulated — ex nihilo nihil fit, "nothing comes from nothing" — continues to be posed, in altered form, in modern physics.

Third, the opposition between the senses and reason. Modern cognitive science has revealed that human perception is shot through with illusions and biases. Parmenides' demand — "Do not trust the senses; judge by reason" — resonates with the basic stance of the scientific method. Special relativity — in which the counter-intuitive structure of spacetime is confirmed by logic and experiment — might be called a modern instance of the Parmenidean spirit.

Fourth, the power and limits of formal systems. Parmenides placed absolute trust in the power of logic. Yet in the twentieth century, Gödel showed that in any sufficiently powerful formal system there exist propositions that can be neither proved nor disproved (the incompleteness theorems, 1931). Logic alone cannot reach all truths — a result that shakes Parmenides' optimism at its foundations. Modern AI, too, is a superlative executor of formal reasoning, and yet whether it truly "understands" meaning or Being remains an open question. The problem Parmenides opened — "Are thought and Being the same?" — takes on an unprecedented urgency in the philosophy of artificial intelligence.

Questions for the Reader

• Is change truly real? Or is the sensation of change merely an appearance produced by human cognition? What would Parmenides make of the "block universe" hypothesis in physics, according to which past, present, and future are equally real?
• Is it possible to speak about "nothing"? The moment we say "nothing does not exist," are we not already making something an object of thought? How should we think about this paradox of language?
• When science leads to conclusions that defy common sense — time dilation, wave–particle duality — should we trust the senses or reason? How far does Parmenides' stance apply to modern scientific realism?

References

• (Primary sources): Diels, H. & Kranz, W. Die Fragmente der Vorsokratiker, 6th ed., 1951. (DK 28B fragments) — Standard edition of Pre-Socratic fragments
• (Primary sources): Coxon, A.H. The Fragments of Parmenides. Rev. ed., Las Vegas: Parmenides Publishing, 2009. — Definitive critical text and commentary
• (Study): Gallop, David. Parmenides of Elea: Fragments. Toronto UP, 1984. — Greek text, English translation, and commentary; a standard introduction
• (Study): Kirk, G.S., Raven, J.E. & Schofield, M. The Presocratic Philosophers. 2nd ed., Cambridge UP, 1983. — Standard overview of Pre-Socratic philosophy
• (Study): Mourelatos, Alexander P.D. The Route of Parmenides. Rev. ed., Las Vegas: Parmenides Publishing, 2008. — Analysis of the structure and logic of Parmenides' poem
• (Study): Curd, Patricia. The Legacy of Parmenides. Las Vegas: Parmenides Publishing, 2004. — The principal work advancing the "predicational monism" interpretation
• (Study): Palmer, John. Parmenides and Presocratic Philosophy. Oxford UP, 2009. — A comprehensive study situating Parmenides' fragments within Pre-Socratic philosophy as a whole
• (Study): Heidegger, Martin. Parmenides (GA 54). Klostermann, 1982. — Lecture course on Parmenides
• (Overview): Stanford Encyclopedia of Philosophy, "Parmenides" (John Palmer). https://plato.stanford.edu/entries/parmenides/