How should we understand Heraclitus's claim that opposites are one?
Does this claim commit him to inconsistency?



Heraclitus of Ephesus (ca. 535 -- 475 BCE), known as "The Obscure", was a pre-Socratic Ionian philosopher, a native of Ephesus on the coast of Asia Minor (present day Turkey)(1).   According to Diogenes Laertius (circa 3rd century CE)(2), a biographer of the ancient Greek philosophers, in the sixth century BCE, Heraclitus of Ephesus wrote a philosophical work entitled "On Nature".   None of the original work has survived.   Only 139 disjointed fragments remain as quotations in the works of others.   Also according to Diogenes, Heraclitus was a misanthrope who had a very low opinion of the intelligence of his fellow Ephesians.   He made a point of writing in an obscure and complex fashion, making extensive use of poetical metaphors and plays on words, so that none but the already knowledgeable could understand him.   As a consequence, many of the remaining extant fragments can be read in more than one way, making it very difficult to tease a coherent interpretation out of the little that remains of his text.

Heraclitus's Milesian predecessors (Thales, Anaximander, Anaximenes, Xenophanes) tried show how the order of the world had come into being, and how it was maintained.   Thales supposedly held that the world originated from water.   Anaximander conceived of the world order as governed by the primordial Boundless.   Xenophanes replaced the Boundless with an intelligent deity who moves all things by thought.   Anaximenes held that the air, with its universal presence, its association in popular culture with life and growth, and its variegated contents, is the foundation of all that exists.

Heraclitus, in contrast, denied that the order (the "logos") is imposed upon the world from without.   Instead, he identified fire as the "ever-living", and "ever was and is and will be"(B30) foundation of all that is.   Heraclitus described a world "which is the same for all, no one of gods or men has made"as constituted by "ever-living Fire"which participates in the changing of nature "with measures of it kindling, and measures going out".   Heraclitus's choice of fire as a replacement for the air of Anaximenes was not likely motivated by a search for a more suitable fundamental principle.   Nothing is literally derived from fire in the way that many natural things can be seen as derived from Anaximenes'air (winds, clouds, water, life).   Heraclitus'aim, therefore, was most likely not to improve upon his predecessors'metaphysics, but to provide a shift in perspective.   His Milesian predecessors focussed on the unchanging order of the world, and sought to explain that.   Heraclitus focussed instead on the change in the world, and sought to explain that.   The advantage of fire for this new point of view is that it the arch-type of something that remains the same by changing.   Like the river with its flowing waters (B12), a fire consists of a constantly changing composition of elements while remaining unchanging in its essence.  

On those who enter the same rivers, ever different waters flow. (B12)

Though the waters are always changing, the rivers stay the same.   Indeed, it is precisely because the waters are always changing that there are rivers at all, rather than lakes or ponds.   It is not that everything is changing, but that some things change to make possible the continued existence of other higher-order things.   But this understanding got lost beneath the "traditional"interpretation of Heraclitus initiated by Plato.

Plato and the "Traditional" Interpretation

Plato applied to his understanding of Heraclitus a notion of "knowledge"as something that is necessarily eternal.   Plato believed that knowledge can only be true knowledge if what it asserts is not merely true for one moment of reality, but for all time.   When you combine this notion with the suggestion that all things are always changing in their elements while remaining unchanging in their essence, you get Plato's   "traditional"interpretation of Heraclitus's theory as a "Theory of Flux".   In the Cratylus, Plato has Socrates say --

"Heraclitus is supposed to say that all things are in motion and nothing at rest; he compares them to the stream of a river, and says that you cannot go into the same water twice."(Cratylus, 402a)

Here Plato is focussing on the ever-changing elements, at the expense of the unchanging essence.   He therefore interprets Heraclitus as arguing that everything is constantly changing.   (Perhaps helped along in this belief by Cratylus, who as a disciple of Heraclitus, is supposed to have argued the same thing.)   Plato understands Heraclitus to be saying that our familiar world is constantly changing, like the river waters flowing past the onlooker.   He reads into Heraclitus the argument that all the things that exist are either coming into existence or going out of existence.   In the Symposium, Plato offers an excellent description of his view of the unstable world of change:

"Even during the period for which any living being is said to live and retain his identity - as a man, for example, is called the same man from boyhood to old age - he does not in fact retain the same attributes, although he is called the same person: he is always becoming a new being and undergoing a process of loss and reparation, which affects his hair, his flesh, his bones, his blood and his whole body. And not only his body, but his soul as well. No man's character, habits, opinions desires pleasures pains and fears remain always the same: new ones come into existence and old ones disappear."(Symposium, 207d)

Plato's interprets Heraclitus as arguing that an ever-changing Flux is the only possible description of the world.   How then, Plato reasons, could one know something truly if it were always changing?   Plato believes therefore that Heraclitus'description of a constantly changing physical universe cannot be the description of what reality is.   He supports this conclusion by maintaining that knowledge is not dependent on the sensible world that is constantly changing, but on another realm of existence altogether.   In the Phaedo dialogue, Plato argues that the "other"world (the world of Forms) is "pure and everlasting and immortal and changeless"(Phaedo 79d)   In the Timeaus, Plato claims that knowledge is of what is exempt from becoming (Timeaus 27d-28a).   Since Plato accepts Heraclitus's arguments that sensibles are not exempt from becoming, he concludes there can be no knowledge of them (Timeaus 52a).   He employs similar arguments in the Republic (479a-d) to show that sensible things, because they are always changing, cannot be the primary objects of knowledge.   Knowledge, therefore, must be of something unchanging -- the Forms (Timeaus 52d).   Plato thus adopts a "two-worlds"view of reality.   One world is the ever-changing world of the sensible -- the Heraclitean world of Flux in all things.   The other world is eternal and unchanging -- the world of the Forms.

Plato's interpretation of Heraclitus has become the "traditional"one, because his philosophical successors (particularly Aristotle) assumed that his interpretation was the right one.   But is it?   I think not.   Plato has only taken one side of the story.   Although many of the remaining extant fragments certainly can be read as arguing that everything is changing, they can also be read as emphasizing that within change there is unity.   In fact Plato must have been aware of this alternative interpretation because he quotes a relevant Heraclitean fragment (B51) in the Symposium (186e-187b).   Both Plato and Aristotle attribute to Heraclitus the doctrine of the "unity of opposites".   And Aristotle goes further, arguing that this doctrine is in fact inconsistent.   In particular, Aristotle, following Plato, argued that Heraclitus'doctrine of the Unity of Opposites violated a fundamental principal of logic - the Law of the Excluded Middle, also known as the Law of Non-Contradiction.   In Aristotle's own words -

"The statement of Heraclitus, that everything is and is not, seems to make everything true, but that of Anaxagoras, that an intermediate exists between two contradictories, makes everything false; for when things are blended, the blend is neither good nor not-good, so that it is not possible to say anything truly."(3)

Hence, the query in the essay title about whether Heraclitus'claim that opposites are one commits him to inconsistency.

Heraclitus -- The Unity of Opposites

There are at least four different ways in which Heraclitus treats what are generally considered to be opposites.   And none of them need be interpreted in the way suggested by Plato and Aristotle.

  1. Perspective: The same thing is often viewed with opposite appreciation or justifies opposite descriptions depending on one's point of view.   From B13, pigs like mud, but men do not.   From B9, horses, dogs, and humans have different notions of pleasure.   Asses prefer straw to gold, while men prefer gold to straw.   From B61, the sea is pure for the fish, but impure for man.   From B60, the way up and the way down is one and the same, the difference depending on one's direction of travel.   From B48, the bow is called life (in a play on words), yet its function is death.   From B58, the work of the surgeon merits a fee (is good) to the surgeon, but is painful (evil) to the patient.   From B103, the beginning and the end of the circumference of a circle are the same.   There is only one thing, yet there can be opposite descriptions of it depending on one's point of view.
  2. Contrast: Good (and bad) things are recognizable only if we also recognize their opposites.   Things are often defined, recognizable, noticeable only in terms of their opposites.   From B111, health is pleasant and noticeable only because of sickness, good only because of evil, plenty only because of hunger, and so forth.   Things like health and sickness, good and evil, hunger and plenty exist on a scale delineated by opposite extremes.   The scale is one single spectrum, with two opposing limits.   Which limit you see depends on which way you look at the one single spectrum.
  3. Cyclical Evolution: Many pairs of opposites follow each other in cycles, and are hence connected in a larger whole.   From B12, the river is one, yet the water is ever changing.   From B57, day and night are separate components of the daily cycle.   From B88, the soul cycles between the living and the dead, the mind cycles between being awake and asleep, the body cycles between being young and old.   From B126, thing cycle between being warm and cold, wet and dry.   This sort of cyclical change presupposes the non-identity of the terms.   What Heraclitus suggests here is not the identity of opposites but the fact that they replace each other in a series of transformations: they are not identical, yet are transformationally equivalent.   Things change in the details, yet remain the same in essence.  
  4. Tension of Opposing Forces: Some opposing things exist in dynamic equilibrium.   From B51, the function of both bow and lyre are dependent on the dynamic tension ("backwards-turning attunement") of opposing forces.   The opposing forces are the detailed elements that exist within and make possible the one higher-level thing.  

From these four different ways in which Heraclitus describes how opposites relate to each other, one can easily conclude that opposites do not really exist as separate things.   Only the unitary underlying object, spectrum, or process exists.   There are opposites which are coinstantiated within a single invariant object.   And there are opposites which are coninstantiated within a single invariant process.   The road which can be both the way up and the way down (B60) and the dynamic tension of bow and lyre (B51) exemplify the coinstantiation of opposites in a single thing.   Whereas the unity of day and night, winter and summer, surfeit and hunger (B67) exemplify the coinstantiation of opposites in a unitary cyclical process.  

What appear to be opposites are but different aspects of an underlying hidden unity.   The fragments thus suggest that Heraclitus does not believe that opposites are one (unity or identity), but rather believes that opposites can be present in the same thing, or coinstantiated.   That is, that one and the same thing may be both hot and cold, pure and polluted, etc. depending on where along the one unifying spectrum one chooses to focus one's point of view.   Alternatively, one and the same thing may be both day and night, wet and dry, pulling and pushing, etc. depending on whether one chooses to focus on the details, or on the higher level structure.

The change that all things experience is driven, according to Heraclitus, by the strife between those opposites that are coinstantiated within any given object (B80, B53).   Beneath an object's apparently motionless exterior is a tension between opposed forces.   This is not obvious to us only because, as Heraclitus also tells us, 'nature loves to hide'(B123) and 'an unapparent connection (harmonia) is stronger than an apparent one'(B54).   Against his predecessors'notions of the world as a fixed unity, Heraclitus presents the world as process.   For Heraclitus, the great truth is that the unity of the world-order ("logos") depends on difference, opposition, and change along a spectrum or through a cycle.   But the process of change is an ordered one, governed by fundamental principles.   Thus, universal change is accompanied by an eternal unchanging governing canon -- the "logos".

In general, therefore, what we see in Heraclitus is not a conflation of opposites into an identity as is suggested by the phrases "unit of opposites"or "opposites are one", and the interpretation of Plato and Aristotle.   What we see instead is a series of subtle analyses revealing the interconnectedness of contrasting states in life and in the world.   There is no need to ascribe to him the kind of logical fallacy suggested by Plato and Aristotle.   Heraclitus would assuredly admit that opposites are a reality, and that correlative opposites are not identical to each other.   But he would equally assuredly maintain that their interconnections are real -- opposites exist as part of a spectrum, part of a cyclical process, or as elements of a higher-level entity.   His claim is that opposites exist as but parts of a larger unity, to be seen separately only as our perspective changes its focus.   This claim does not commit him any logical inconsistency.


EndNotes & References

(1)     Wikipedia contributors. Heraclitus. Wikipedia, The Free Encyclopedia. September 26, 2007, 03:04 UTC.   URL=

(2)     Diogenes Laertius, The Internet Encyclopedia of Philosophy, URL=<

(3)     Aristotle, Metaphysics, trans. Hippocrates G. Apostle, Bloomington, Ind., 1966. Book IV, 1012a25-29.

Graham, Daniel W., "Heraclitus", The Stanford Encyclopedia of Philosophy (Spring 2007 Edition), Edward N. Zalta (ed.), URL =                                         <>.

Kirk, G. S., "Natural Change in Heraclitus", Mind, New Series, Vol. 60, No. 237. (Jan., 1951), p 38.

Kirk, G.S., Raven, J.E., Schofield, M., The Presocratic Philosophers, 2nd ed., Cambridge University Press, Cambridge, England, 1957.


Appendix -- Selected Fragments from Heraclitus

B9             For a horse, a dog and a human being have different pleasures; asses prefer straw to gold, since asses find food sweeter than gold.

B10           Graspings: things whole and not whole, what is drawn together and what is drawn asunder, the harmonious and the discordant. The one is made up of all things, and all things issue from the one.

B12           On those who enter the same rivers, ever different waters flow.

B13           Pigs delight in the mire more than in clean water.

B30           This world, which is the same for all, no one of gods or men has made. But it always was, is, and will be: an ever-living Fire, with measures of it kindling, and measures going out.

B36           For it is death to souls to become water, and death to water to become earth. But water comes from earth; and from water, soul.

B48           The bow (βιός) is called life (βίος), but its work is death.

B51           They do not understand how, though at variance with itself, it agrees with itself. It is a backwards-turning attunement like that of the bow and lyre.

B53           War is father of all and king of all; and some he manifested as gods, some as men; some he made slaves, some free.

B54           An unapparent connection (harmonia) is stronger than an apparent one.

B57           Men are sure that [Hesiod] he knew very many things, he who did not know day and night: they are one.

B58           And good and evil are the same. For doctors, cutting and burning and torturing sick men in every way, still complain that they do not receive as much pay as they deserve from the sick, producing the same things, goods and sicknesses.

B59           The straight and the crooked path of the fuller's comb (γναφεῖον) is one and the same.

B60           The way up and the way down is one and the same.

B61           The sea is the purest and the impurest water. Fish can drink it, and it is good for them; to men it is undrinkable and destructive.

B62           Mortals are immortals and immortals are mortals, the one living the others' death and dying the others' life.

B67           God is day and night, winter and summer, war and peace, surfeit and hunger; but he takes various shapes, just as fire, when it is mingled with spices, is named according to the savor of each.

B80           We must know that war is common to all and strife is justice, and that all things come into being through strife necessarily.

B84a         It rests by changing.

B88           And it is the same thing in us that is quick and dead, awake and asleep, young and old; the former are shifted and become the latter, and the latter in turn are shifted and become the former.

B103         In the circumference of a circle the beginning and the end are common.

B111         It is sickness that makes health pleasant and good; hunger, plenty; weariness, rest.

B123         Nature loves to hide.

B125         Even the posset (barley-drink) separates if it is not stirred.

B126         Cold things become warm, and what is warm cools; what is wet dries, and the parched is moistened

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