52. The Atomists

Democritus, one of the Atomists, among the Abderites
Democritus Among the Abderitans, oil on canvas by François-André Vincent, c. 1790; in the Los Angeles County Museum of Art

Atomic theory has a long, rich life in human history. It’s gone from a metaphysical theory developed by the Presocratics – namely the Atomists – to explain the idea of change vis-à-vis Parmenides’ idea of constant Being, to the modern scientific application of nuclear energy and nuclear warfare.

The dynamic duo of atomism was Leucippus and Democritus. Leucippus, who was from Miletus, was the founder of the atomist school.1 He started in the school of Parmenides, being a disciple of Zeno of Elea. Democritus, who came a little later, was a pupil of Leucippus. As such, of the corpus of work left behind by these two men, it is difficult to know which man wrote what.

Their monumental contribution to philosophy and science is their atomic theory, which states that all matter is made up of infinite, indivisible, eternal, unchangeable, and imperceptible entities.2 The only thing that changes is their position in space.

The question is how did we get from the Atomists’ simple but profound theories to the nuclear technology we have today that can potentially give us an infinite energy supply…or obliterate the world?

The word “atom” in Greek is a combination of a- which means “without” and toma which means “cut” – thus, “without a cut.” In other words, it is the smallest unit of matter which can exist. We know from high school science that an atom is composed of even smaller particles of positively charged protons and negatively charged electrons that, if in balance, give the atom a net neutral charge. So, the modern definition of an atom is the smallest unit that matter can be divided into without the release of electrically charged particles.

The Monists vs. the Pluralists

Again, as I have discussed in my other recent posts, Parmenides, with his concept of unchanging Being, threw down the philosophical gauntlet. He reasoned that Being could not come into or go out of existence so change is impossible. His sidekick, Zeno of Elea, followed up with his paradoxes, demonstrating that motion also is impossible. They concluded that we live in a world of illusion.

As preposterous as this conclusion was, it was nearly impossible to refute. Anaxagoras posited a universal Mind to answer the challenge and Empedocles developed the theory of the four basic elements controlled by the forces of Love and Strife. They both struck out at refuting the theories of Parmenides and Zeno, so it became the Atomists’ turn at bat.

The battle lines were clearly drawn at this point. On one side were the Monists, as represented by Parmenides and the Elean school in Southern Italy, and on the other side were the Pluralists, as represented by the Ionian school to the east. What these early Greek philosophers were doing is bringing into focus the most fundamental problem of philosophy – the metaphysical tension between the One and the Many, also known as the Problem of Universals.

The Atomists Attempt to Answer Parmenides

As mentioned above, Leucippus of Miletus was the founder of the atomist school, a former student of the school of Parmenides, and a disciple of Zeno of Elea. As with many teacher-student relationships, the most famous being Plato and Aristotle, the student will often go on to develop ideas contrary to the teacher, and so it was with Zeno and Leucippus. Leucippus took a position contrary to Parmenides and Zeno to try to refute them. He and Democritus did this by building upon the work of their contemporary, Empedocles.

Even though Empedocles failed to adequately answer Parmenides, his theory had enough substance in it to form the basis of atomic theory, which is really a logical development of Empedocles’ ideas.3 Empedocles did not develop his doctrine of particles to the fullest extent, nor did he, as author Frederick Copleston states, “carry the quantitative explanation of qualitative differences to its logical conclusion.”

The following quote from Copleston sums up how the Atomists continued the work of Empedocles via their own theories:

The philosophy of Empedocles formed a transitional stage to the explanation of all qualitative differences by a mechanical juxtaposition of material particles in various patterns. Moreover, Empedocles’ forces – Love and Strife – were metaphorical powers, which would have to be eliminated in a thorough-going mechanical philosophy. The final step to complete the mechanism was attempted by the Atomists.”4

Leucippus and Democritus Posit Atomic Theory

This is where it really gets interesting. Leucippus and Democritus posited a theory that modern physics has proven to be true. They reasoned that the material universe is made up of an infinite number of indivisible units called atoms. While we know that the number of atoms is not infinite, it is still an incredibly large number. For example, scientists have estimated that there are between 1078 to 1082 atoms in the universe.5 That’s a number between ten quadrillion vigintillion and one-hundred thousand quadrillion vigintillion.

What’s incredible is that they formulated the concept of the atom without any scientific instrumentation. How did they know this intuitively? The answer is that they were simply trying to solve the metaphysical problem that they inherited. If they did this using sound reasoning, then it only makes sense that this would bring them closer to the truth. Contrary to what Descartes and subsequently Kant would say, our minds are indeed made to observe and comprehend the physical world.

The Atomists theories stated that these particles were so small that they could not be seen with the human eye. Because of the lack of scientific instrumentation at that point in time, this would remain just a theory until the 18th century, when scientific experimentation produced strong direct evidence that atoms existed.

Who Were Leucippus and Democritus?

Before we continue with their theories, let’s talk about the lives of these two men who have been dubbed the Atomists. As stated above, not much is know about Leucippus. The philosopher Epicurus seemed to have doubted his very existence, even though historian Diogenes Laertius is the one who stated that he was a student of Zeno.6

Even in 19th century scholarship, there was considerable controversy over his existence, but this was the age of extreme skepticism anyway, where almost everything in the past was doubted and questioned. But I think that in the end, we can have reasonable assurance in the word of Aristotle, who credited Leucippus as the founder of atomism.


Leucippus, another of the Atomists

We know much more about Democritus who, in a way, stole the limelight from his teacher. He was born around 460 B.C. and is reputed to have died at the age of 100.7 If this were true, then he would have died just four years before Alexander the Great was born and he would have been alive when Plato was teaching Aristotle.

Democritus was widely traveled, even as far as India, and wrote extensively on his travels, although, like his other works, very little survives. He was a prolific author, writing on philosophical topics that included metaphysics, ethics, mathematics, and natural science.8 In addition, he wrote on farming, art, medicine, grammar, literature, and military matters.

The Atomists’ Theories: Atoms in a Void

Even though atoms were infinite, indivisible, eternal, unchangeable, and imperceptible, the men did posit that they differ in shape and size and could change position. In addition, they had no quality except impenetrability or solidity.9 Being apparently infinite in number, they moved in a void.

Here they introduce another new concept – the void. The void is a space which separates atoms and within which they can move.10 A void makes motion possible; otherwise, the atoms would be frozen together in one big mass similar to Anaxagoras’ account of the beginning of creation. The Atomists called atoms “What Is,” and the void “What Is Not.” Unlike Parmenides who did not believe that there cannot be nothingness, the Atomists believed in nothingness and believed that it was real.11

The following quote comes from a commentary by the 6th century A.D. Neoplatonist Semplicius on Aristotle’s work, On Democritus. I find it remarkable, almost astounding, how it specifically describes, albeit in rudimentary form, the basic principles of modern chemistry:

“Democritus thinks that the nature of eternal things consists in small substances, infinite in quantity, and for them he posits a place, distinct from them and infinite in extent. He calls place by the names ‘void’…and that they [the atoms] possess all sorts of forms and all sorts of shapes and differences in magnitude. From them, as from elements, he was able to generate and compound visible and perceptible bodies. The atoms struggle and are carried about in the void because of their dissimilarities and the other differences mentioned, and as they are carried about they collide and are bounded together in a binding which makes them touch and be contiguous with one another but which does not genuinely produce any other single nature whatever from them; for it is utterly silly to think that two or more things could ever become one. He explains how the substances remain together in terms of the ways in which the bodies entangle with and grasp hold of one another; for some of them are uneven, some hooked, some concave, some convex, and others have innumerable other differences. So he thinks that they hold on to one another and remain together up to the time when some stronger force reaches them from their environment and shakes them and scatters them apart. He speaks of generation and of its contrary, dissolution, not only in connection with animals but also in connection with plants and worlds – and in general with all perceptible bodies.

– Aristotle Fragment [208]

The Atomists and Physics

In the theories posited by the Atomists, we see the basics of modern physics and chemistry. For example, they explained motion through the presence of a void. Parmenides denied that such a void or nothingness existed. How far off where they?

In 1905, Albert Einstein introduced his idea of special relativity, which basically proposed that motion warps space and time. The important aspect here is the introduction of the idea that time is interwoven with space. Prior to this, time was considered a constant by Newton, and a separate dimension outside the three dimensions of space by Descartes. For the first time, space and time were linked.

Even though Einstein linked space and time – and he did clarify the idea – in 1908, his former college professor, Hermann Minkowski, a German mathematician, linked the two concepts of space and time into what he called “space-time,” thus creating a four dimensional, rather than a three dimensional, universe.12 Many people think Einstein invented this concept while it was actually his former teacher. Unfortunately, whereas Einstein went on to be a rock star, Minkowski faded into obscurity. I include his picture below so that we can remember him.

Hermann Minkowski, Einstein's predecessor, built upon the atomic theory of the Atomists
Herman Minkowski, the inventor of the concept of space-time

As a case in point about Einstein’s popularity: As I write this post, a news story just broke (November 24, 2021) that a manuscript containing Einstein’s handwritten notes of his general theory of relativity was auctioned off in Paris for $13 million dollars (11.6 million euros) – four times the expected amount – surpassing all previous records. Below is a photo of the first page of the manuscript. You can read the full story by clicking the link in the footnotes below.13 Once again, Einstein eclipses Minkowski.

Pages of a manuscript on the theory of general relativity of Albert Einstein, who really was taking atomic theory a step further.
Page 1 of Einstein’s manuscript on general relativity (Alain Jocard/AFP)

What does all this have to do with the Atomists’ theories? Parmenides left out both space and void, which is why he painted himself into a corner. The Atomists came much closer by including space, but they left out time. Even though they omitted time, they pretty much nailed the idea that motion is related to space; they just couldn’t explain why because they did not have the mathematical tools at their disposal.

I’ll end this section with part of a quote by physicist John Wheeler in describing Einstein’s general theory of relativity:

“Space-time tells matter how to move.”14

If we leave out the word “time,” we get “space tells matter how to move,” which comports with the Atomists, who said that the motion of atoms was made possible by a void.

The Atomists and Chemistry

I have enjoyed chemistry since high school and it is one of the reasons I majored in biochemistry in college. So, I particularly like this section.

In the above fragment of Aristotle, I see remarkable parallels between the Atomists’ theories and modern chemistry. For example, they say that:

“…[the atoms] possess all sorts of forms and all sorts of shapes and differences in magnitude.

Presently, there are 118 known elements on the periodic table, 92 (some say up to 98) of which are found to exist naturally; the rest are man-made. What distinguishes these elements from one another is the number of protons in their nuclei, known as the atomic number. This gives the elements different “shapes” and “sizes” relative to their atomic weights. Again, this is very close to the Atomists’ description, which is remarkable considering that they had no scientific instruments. We know today, of course, that the number of valence electrons is also important in determining how elements combine.

Next, Aristotle says:

From them, as from elements, he was able to generate and compound visible and perceptible bodies.”

Here we have the idea, although in rudimentary form, that elemental atoms join together to make compounds – “elements” join together in “compound visible bodies” – a basic premise of chemistry.

Then, he says:

“…the substances remain together in terms of the ways in which the bodies entangle with and grasp hold of one another; for some of them are uneven, some hooked, some concave, some convex, and others have innumerable other differences.”

They seem to be describing the fact that there are different types of “chemical bonds.” We know from high school chemistry that there are two basic types of chemical bonds: ionic and covalent.

This next quote is remarkable:

…they hold on to one another and remain together up to the time when some stronger force reaches them from their environment and shakes them and scatters them apart.

Now we have chemical compounds that are broken apart into basic elements by a “stronger force.” The example that comes to mind for me is burning wood in our wood stove at home. Wood is made of cellulose. When a “stronger force” like fire comes along and burns the wood, it cleaves the bonds between the atoms of the cellulose, thus releasing stored energy that helps fuel the fire. This is denoted by the following formula:


The one point in the above fragment where they hit a foul ball is as follows:

“…which makes them touch and be contiguous with one another but which does not genuinely produce any other single nature whatever from them; for it is utterly silly to think that two or more things could ever become one.”

They could not conceive of atoms combining in such a way to make a compound so unified as to create a substance having an entirely new nature. We know now that this happens all the time. Take the elements of sodium and chlorine. Sodium (Na) is found in nature, but always in compounds with other elements. Think about chlorine (Cl2) that is used in pools. Imagine drinking pure chorine. If you did, you would not be around very long.

But combine chlorine with sodium and you get sodium chloride – table salt.


The elements indeed have become one; they created a new compound which has a new nature.

Did the Atomists Answer Parmenides?

In order to refute Parmenides, the Atomists had to demonstrate that motion was possible without violating the unchanging nature of Being. The question is did they do it? In his Metaphysics, Aristotle seems to have thought no:

“Concerning the origin and manner of motion in existing things, these men also [the Atomists], like all the others, lazily neglect to give an explanation.”15

Metaphysics Book Alpha 4, 185b

But in fragment 208 above, he does assert that they did provide an explanation for movement, which is the void:

The atoms struggle and are carried about in the void because of their dissimilarities and the other differences mentioned.”

Rather than being lazy, they were simply trying to provide a naturalistic explanation of motion without resorting to the quasi-mythological explanation of Empedocles’ Love and Strife. The Atomists’ theories were simply positing a void that made motion possible without dealing with the question of origins, which no Greek philosopher, including Aristotle, ever answered adequately. They answered “what” made motion possible without concerning themselves with the “how.”

I believe that the Atomists answered Parmenides’ challenge – even if not completely – far better than any of their contemporaries’ theories. In a metaphysical judo move, the Atomists used the arguments of Parmenides and Zeno against them. Parmenides said that plurality was impossible because everything would have to have the properties of the One.16 The Atomists agreed with monism and defended pluralism at the same time. They simply asked why there couldn’t be a plurality of atoms, each having the same metaphysical properties as the One. In regard to Zeno’s claim of infinite divisibility, they agreed and said that there were an infinite number of atoms.

From a modern perspective, the Atomists answered Parmenides by adding the element of space to matter, thus expanding Parmenides’ one dimensional, truncated universe to include not only Being but matter, space, and as a natural consequence, motion as well. Anaxagoras and Empedocles made the error of trying to play in an extremely small arena as defined by Parmenides, whereas the Atomists expanded the arena and added more players.

The Atomists made great progress, but unfortunately, there would not be another major breakthrough in cosmology until 1908 when that obscure German mathematician, Herman Minkowski, would add the element of time as the missing piece of the puzzle.

The Legacy of the Atomists’ Theories

The Atomists and their scientific theories were the high water mark of Presocratic philosophy. Some say that the three biggest contributions to Greek philosophy were made by Plato, Aristotle, and the Atomists.17 The Atomists inspired Epicurean theory as well as the Latin metaphysical poem “De Rerum Natura,” written by Lucretius.18 Scholar Jonathan Barnes praises atomism as “the culmination of early Greek thought.”

More importantly, the Atomists have had a significant impact on modern science. The Atomists’ theories were resurrected in the 17th century by French philosopher and scientist Pierre Gassendi (1592- 1655).19 He applied the Atomists’ theories to physics, metaphysics, and even ethics.

The English chemist John Dalton (1766–1844) discovered that reactants in a chemical reaction always have the same mass ratio, providing strong evidence that there were such things as atoms and molecules. As knowledge of elements and compounds grew, Dmitri Mendeleev (1834-1907), the great Russian chemist, eventually came up with an ingenious way of arranging elements based upon their properties called the periodic table of elements. By using this table, Mendeleev was able to predict elements that were not known at the time.

In 1827, Scottish botanist Robert Brown noticed that tiny pollen grains suspended in water moved about in complex paths. From this, he determined that the movement of the pollen grains was caused by collisions with molecules of various sizes. Even though most scientists at the time believed in the existence of atoms, Brownian motion was the first conclusive, direct evidence.20

In 1905, Einstein theorized that Brownian motion could be used to determine the size of individual atoms and molecules, and French physicist Jean-Baptiste Perrin (1870–1942) used Einstein’s theory to actually measure the size of various atoms and molecules. He then made numerous scientific applications from this, eventually winning the 1926 Nobel Prize.

And of course, starting in the 20th century, many applications using atomic theory have been found, both beneficial and destructive. Nuclear technology is utilized for clean energy production as well as applications in medicine. We also know of the potential destructiveness of nuclear technology if used unethically or incorrectly. Who would have ever thought that one of the smallest particles known to man could yield so much power?

An Atom Seen for the First Time

I end with the story of Professor Erwin Mueller (1911 – 1977), a German-born physicist who studied under Nobel Prize winner Gustav Hertz.21 He came to America and joined the faculty of the University of Pennsylvania in 1951. Shortly after, in 1955, he invented the field ion microscope after only a year’s effort, which made it possible to make pictures of atoms for the first time.

He recounted the story as follows:

“It was a sticky day in August that I became the first person to see an atom. On that day, the regular array of atoms and a crystal lattice became clearly visible through the field ion microscope which I had developed.”22

Who would have ever thought that 2300 years after Democritus made his claim about the existence of atoms that were “too small to be perceived by the senses” that a relatively unknown physicist by the name of Erwin Mueller would actually see one?

Do you have any thoughts on atomism? Please leave your comments below and don’t forget to subscribe. Thank you!

Deo Gratias

Featured Book

From Amazon: “This concise book introduces non-physicists to the core philosophical issues surrounding the nature and structure of space and time, and is also an ideal resource for physicists interested in the conceptual foundations of space-time theory. Tim Maudlin’s broad historical overview examines Aristotelian and Newtonian accounts of space and time, and traces how Galileo’s conceptions of relativity and space-time led to Einstein’s special and general theories of relativity. Maudlin explains special relativity with enough detail to solve concrete physical problems while presenting general relativity in more qualitative terms. Additional topics include the Twins Paradox, the physical aspects of the Lorentz-FitzGerald contraction, the constancy of the speed of light, time travel, the direction of time, and more.”

Footnotes and Endnotes:

  1. Copleston S.J., Frederick, A History of Philosophy, Book One, pp. 72-73, An Image Book, Doubleday, 1985
  2. Grayling, A.C. The History of Philosophy, Penguin Press, p. 48, New York, 2019
  3. Coppleston S.J., Frederick, A History of Philosophy, Book One, pp. 72-73
  4. Ibid.
  5. Kiernan, Patrick, “Which is greater? The number of atoms in the universe or the number of chess moves?” National Liverpool Museums
  6. Berryman, Sylvia, “Leucippus,” The Stanford Encyclopedia of Philosophy (Winter 2016 Edition), Edward N. Zalta (ed.)
  7. Grayling, A.C. The History of Philosophy, Penguin Press, p. 48
  8. Ibid.
  9. Coppleston S.J., Frederick, A History of Philosophy, Book One, p. 73
  10. Grayling, A.C. The History of Philosophy, Penguin Press, pp. 48-49
  11. Please see Post 23 on Hesiod where I go into more detail on the concepts of something and nothing.
  12. Click this link for the original lecture: https://en.wikisource.org/wiki/Translation:Space_and_Time
  13. “Rare Einstein notes on theory of relativity sell for record $13 million,” The Times of Israel, by AFP, 24 November 2021, 12:46 am
  14. Webb, Richard, “General Relativity, Einstein’s Theory of How Gravity Warps Space and Time,” New Scientist
  15. Grayling, A.C. The History of Philosophy, Penguin Press, p. 49
  16. Ibid, p.50
  17. Ibid, p. 50-51
  18. See poem here http://classics.mit.edu/Carus/nature_things.html
  19. Fisher, Saul, “Pierre Gassendi,” The Stanford Encyclopedia of Philosophy (Spring 2014 Edition), Edward N. Zalta (ed.)
  20. “Discovery of the Atom,” lumen
  21. Bamberger, Warren, “Prof. Erwin Mueller, 65; Physicist Was First Person to See an Atom,” The New York Times, May 18, 1977
  22. Ibid.


Ball, Fred, The Elements: A Visual History of Their Discovery, University of Chicago Press; First edition (September 6, 2021)

Copleston S.J., Frederick, A History of Philosophy, Book One, An Image Book, Doubleday, 1985

Diogenes Laertius, Lives of Eminent Philosophers, translated by C.D. Yonge, Digireads.com Publishing, 2020

Diogenes Laertius, Lives of Eminent Philosophers, translated by Pamela Mensch and edited by James Miller, Oxford University Press, 2018

Grayling, A.C. The History of Philosophy, Penguin Press, New York, 2019

Greene, Brian, The Elegant Universe: Superstrings, Hidden Dimensions, and the Quest for the Ultimate Theory, W. W. Norton & Company; Reprint edition (October 11, 2010)

Greene, Brian, The Fabric of the Cosmos: Space, Time, and the Texture of Reality, Vintage Press, February 8, 2005

Maudlin, Tim, Philosophy of Physics: Space and Time (Princeton Foundations of Contemporary Philosophy), Princeton University Press; Reprint edition (May 26, 2015)

Internet Resource:

Adamson, Peter, “The Final Cut: Democritus and Leucippus,” History of Philosophy Without Any Gaps, King’s College, London, 16 January 2011

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