Early Atomic Theories

Thoughts of Existence Pave the Way for Atoms

The ancient Greek philosophers played a significant role in shaping the initial thoughts about atoms and early atomic theories. Several of the ancient philosophers pondered and developed a theory of matter, with one even imagining the existence of a fundamental building block that made up not only all living and nonliving things, but the supernatural as well. Their thoughts were speculative and philosophical, rather than scientific in nature. And while they attempted to touch on the nature of matter and its composition, their real goal was to address something of profound concern to the ancient Greeks: the nature of permanency and change. Unfortunately, these “theories” of matter were rather short-lived. Although there was some revival during the Middle Ages and the Renaissance, they never gained any real momentum until the seventeenth century.

Early Atomic Theories

The early atomic theories focused on a primary element responsible for creating all other matter. Heraclitus said it was fire, Thales of Miletus (c. 624 BC–c. 546 BC) said it was water, Anaximenes (c. 585 BC–c. 528 BC) thought it was air, and Empedocles finally unified these, declaring there to be four elements: air, earth, fire, and water. Later, Aristotle adopted Empedocles’ four elements, and so it remained until about the seventeenth century.


Born in Acragas, in present-day Sicily, Empedocles (c. 492 BC–c. 432 BC) was an interesting character, who has been described as a philosopher, prophet, healer, democratic politician, mystic, charlatan, fraud, and scientist. His main contribution to the physical sciences was his four-element theory.

These fundamental elements, which he called “roots,” combined in varying amounts to form all other matter: plants, animals, humans, rocks – everything. And while the elements mixed together to form other things, they still maintained their own individual characteristics. Indeed, Empedocles envisioned the four elements as changeless, eternal, and indestructible. Empedocles believed in two eternal metaphysical forces: Love and Strife. Love was responsible for bringing the elements together in the process of creation, whereas the opposing force of Strife was responsible for the separation of the elements, ultimately leading to the process of decay. The cosmic battle between Love and Strife represented the natural cycle of change in the universe; Love built things up and Strife tore them back down, and they struggled against each other, each one trying to gain dominance over the other.

In Empedocles’ theory, we clearly see the concept of a changing universe similar to that described by Heraclitus, although where Heraclitus only believed in Strife, Empedocles softened his theory with the addition of Love as its cosmic counterpart. Perhaps less clear is that Empedocles also embraced a bit of the doctrine of Parmenides. While he didn’t believe in a changeless universe, as Parmenides’ monistic dogma had demanded, he did attribute changelessness to his fundamental elements. To be sure, this was a deliberate attempt to reconcile the opposing doctrines of Heraclitus and Parmenides, and he was not the only one to do so. Nonetheless, he abandoned Parmenides’ monistic view in favor of a pluralistic one governed by his four elements (roots), two forces, and the ensuing comingling thereof. A contemporary of Empedocles and fellow early atomic theorist was Anaxagoras.


Anaxagoras (c. 500 BC–c. 428 BC) was born in the town of Clazomenae in Ionia, located in present-day Turkey. He was the first to bring philosophy to Athens (most likely convinced to come by Pericles (c. 495 BC–c. 429 BC) who became his student) and spent thirty years there but eventually left. It seems his teachings on the Earth, the Sun, and the Moon might have gotten him into a bit of trouble (apparently Galileo wasn’t the first to suffer this fate). Specifically, he was in violation of a law permitting the impeachment of anyone who didn’t practice religion and taught theories about the heavenly bodies. He was charged for impiety.  Rather than stay and face his sentence, which was execution, with the assistance of Pericles he left Athens for Lampsacus (in Asia Minor), where he remained for the rest of his life.

Like Empedocles, Anaxagoras attempted to meet the challenge of Parmenides’ demand of a changeless world while accounting for the apparent change we experience in everyday life. Whereas Empedocles singled out air, earth, fire, and water as the fundamental building blocks of everything in existence, Anaxagoras, seeing no reason for such discrimination, declared that everything contains a bit of everything else.

For Anaxagoras, things such as bone, skin, and hair were just as real as Empedocles’ fundamental elements of air, earth, fire, and water, and as such there’s no reason one would choose some in favor of others. So he decided not to choose, but instead included a “portion of everything in everything.” While it’s not known for sure, it might be that he arrived at his theory of matter from his rather insightful studies in nutrition. Anaxagoras noted that food provided nourishment for animals that, in turn, caused certain things to occur, such as their hair to grow and their skin to heal. He concluded that food must then have the constituents of hair and skin already in it to be able to convey these effects.

Moreover, Anaxagoras considered matter to be infinitely divisible. Thus, if one cut a piece of hair again and again, it would still contain the essence of hair. He says, “For of the small there is no smallest, but always a smaller (for what is cannot not be). But also of the large there is always a larger, and it is equal in amount to the small. But in relation to itself, each is both large and small.”

However, despite this, Anaxagoras considered these components of matter, often referred to as “seeds,” or “stuffs,” as eternal and indestructible, albeit more loosely so than envisioned by Empedocles. This still raises the question that if everything contains everything else (in varying proportions nonetheless), then what is it that makes something what it is? To this Anaxagoras replies: “each single thing is and was most plainly those things of which it contains most.” In other words, something is what it is because it contains most of that “stuff.” More precisely, something is what it appears to be macroscopically because it contains most of that “stuff” microscopically.

So we see in both the theories of Empedocles and Anaxagoras the attempt at producing intelligible theories of matter. Each tried to combine ideas that would account for the changing world that we all experience, while still allowing for certain components to remain fundamental, and as such changeless. In effect, each was trying to include simultaneously, in his unique way, the dogma imparted by Heraclitus and Parmenides.

Today, their ideas may sound strange and metaphysical to us, yet one can find the similarity between them and current atomic theory. This is perhaps best exemplified in the theory put forth by Democritus, who is undoubtedly the most important ancient Greek atomic theorist.

Democritus’ Atom

Democritus (c. 460 BC–c. 370 BC) was a native of Abdera in Thrace, located in present-day Greece. He travelled widely, perhaps spending time in Egypt and Persia. He also spent time in Athens: “I went to Athens and no one knew me.”

Indeed, it seems that in Athens Democritus never really fit into the intellectual elite, and his philosophy was ignored for some time. Nonetheless, his wealth of knowledge and exactness of thinking give him a much-deserved place in the history of philosophy. By our present-day standards, he was perhaps the most successful of the ancient Greek philosophers with regards to the remarkable accuracy of his ideas. For example, he considered the Milky Way to be a collection of tiny stars, and the Moon to be very much like the Earth in that it contained mountains and valleys. Regardless, we know him primarily for his atomic theory.

Democritus was a student of Leucippus (fifth century BC), who had an atomic theory of his own. In fact, it’s hard to untangle the atomic theories of Democritus and Leucippus. This is mostly because we know very little about Leucippus, and it has been speculated that he never actually existed, although this seems unlikely since Aristotle and Theophrastus (c. 371 BC–c. 287 BC) mentioned his atomic theory explicitly. It seems more likely that Leucippus set in place some of the fundamentals, and that Democritus built upon them, thereby extending the overall theory.

Democritus considers everything in the universe – including the human mind and soul, and even the gods – to be made up of atomos, which is Greek for indivisible and from which we get the word atom. Indeed, Democritus considered these atoms to be indivisible (contrast this with Anaxagoras, who considered his fundamental pieces to be infinitely divisible). He imagined atoms to occur in a variety of different shapes and sizes, which were responsible for the properties found in the objects they made up. Moreover, he considered atoms to be changeless, eternal, and indestructible, similar to the way Empedocles envisioned his four fundamental elements.

Democritus saw material objects as existing in a temporary state, being created or destroyed as atoms come together or fall apart under the influence of natural forces; all that remains, then, are the atoms constituting those material objects. This is not unlike Empedocles’ view, where he imagined the four elements giving rise to material objects under the influence of the forces Love and Strife. In addition, Democritus also gave motion to his atoms.

Democritus imagined atoms as always in motion, undergoing collision after collision with each other as they moved around. Moreover, this motion was a fundamental property and, like the atoms themselves, was eternal and indestructible, although changeable under certain circumstances.

In order for atoms to be in motion, there must be a space for them to move, and thus Democritus invented the void. According to Democritus, atoms move in the void with a constant random motion (he likened the movement of atoms to the dust particles one sees dancing around in the sunlight when there’s no breeze). This is much like how we imagine them doing so today, as described by modern-day kinetic theory.

Recall that in Parmenides’ philosophy, material things have existence because we are able to think of them. He also considers it impossible to think of nothing, and therefore it can’t exist. Thus, Democritus’ void may seem to be in blatant disregard of this tenant, as for all practical purposes it seems to be nothing. However, Democritus saw the void as something: a place independent of the atoms for the atoms to reside and move around in. The real problem is that Parmenides could only imagine material objects as something, whereas Democritus was able to imagine both a material object (the atom) and the space it lived in as being something. Democritus makes his point clear: “Nothing exists except atoms and empty space; everything else is opinion.”

Democritus made concessions to both Parmenides and Heraclitus, just as Empedocles and Anaxagoras did, by imagining a universe consisting of an infinite number of changeless, eternal, and indestructible atoms, always engaged in random collisions with each other, and capable of comingling to form material objects as we know them.

Aside from its remarkable similarity with modern-day atomic theory, Democritus’ atomic theory is redeeming in itself for the very fact that it offers a “mechanical explanation” for matter: matter is made of atoms that move in a void and undergo collisions (where preceding collisions are determined by previous ones) that are governed by certain physical laws of nature.

He invokes no divine intervention in this atomic process, but quite simply he maintains that atoms have always been and always will be in motion, and that physical laws describe this motion. The beauty of such a construct is that it lends itself to a scientific description. That is to say, one can hope to develop a mathematical theory describing the physical laws and then proceed to perform experiments to test this theory.

Obviously, neither the needed mathematics nor the experimental procedures were available to Democritus. Additionally, Democritus’ theory suffered another blow – namely, Aristotle, who stunted the development of Democritus’ work. On several accounts he mentions Democritus’ atomic theory explicitly, only to attack it. Ironically, it’s in this way that we learn much, perhaps the majority, of what we know of Democritus’ atomic theory.

Why Aristotle?

Aristotle (c. 384 BC–c. 322 BC) was born in Stagira, Greece. His father was the personal physician to the King of Macedonia, a position he inherited. Aristotle studied with Plato (c. 427 BC–c. 347 BC) in Athens beginning at the age of eighteen and remained there for nearly twenty years until Plato’s death. In 343 BC, Aristotle became the tutor to Alexander the Great, who was then thirteen, and continued until he was sixteen, when Alexander’s father made him regent at Pella.

Aristotle’s writings provided the first comprehensive system of Western philosophy covering topics in politics, ethics, logic, metaphysics, and science. There was hardly an area he didn’t write about. Believing all of human knowledge couldn’t fall under a single category, Aristotle was the first to divide it into categories. Here, we are interested in Aristotle’s theory of matter and form.

Just as others did, Aristotle sought to rise to Parmenides’ challenge of permanency while maintaining room for change in the world, as Heraclitus had demanded; his theory of matter and form is an attempt at this reconciliation. According to Aristotle, objects as we know them comprise two parts: “matter” and “form.” The form gives a particular arrangement to matter, and it’s by virtue of the form that we identify an object as a “thing”; to know a thing is to have knowledge of its form.

For example, imagine that a sculptor starts with a lump of clay and proceeds to mold it into the shape of a dog. Here the clay is the matter, and the shape of a dog conferred to the clay by the sculptor is the form. Now, imagine the sculptor begins again, transforming the piece of clay, which once held the shape of a dog, into something else, perhaps a cat this time. Clearly, the matter is still the clay, but now the form has changed from that of a dog to a cat. However, the sculptor does not create the form; it was always there. Instead, the sculptor’s efforts merely brought the form and the matter together. According to Aristotle, change results from a change in the form of matter.

Moreover, Aristotle describes such a process as being governed by four causes: material, formal, efficient, and final. These are the axioms governing the way a material object comes to be, and you can think of them in terms of these questions: What’s the material the object is made of? What’s the object? How was the object built? What’s the purpose of the object? The most important of these is the last one, known as the final cause. Indeed, if there were a central tenet underlying Aristotle’s philosophy, it would be the question posed by the final cause.

It’s the final cause that provides a certain goal for the matter as it moves through its various forms. For the most part, it’s the final cause that provides a sense of permanency throughout the overall process. Thus, Aristotle’s doctrine of matter and form attempts to unify the seemingly disparate ideas of change and permanency. Related to Aristotle’s theory of form and matter are the concepts of “potentiality” and “actuality.” Again, consider the sculptor and the clay. When the clay was merely a lump on the sculptor’s workbench, it had only the potentiality to take the form of a dog or a cat, among other things. But when the clay acquired form through the sculptor’s efforts, it increased its actuality. Thus, the more form something has, the greater its actuality is. Aristotle worked these principles into his theology as well, where his version of God is depicted as perfection consisting of pure form and actuality.

Aristotle’s works were rediscovered after the fall of the Roman Empire by the Arab civilization ruling the region spanning from Persia to Spain. Among this group of Arabs were Muslim and Jewish scholars, who translated the works of Aristotle (and virtually every important work in Greek culture, as well as Persian and Indian culture) into Arabic. These translated works were then acquired by medieval Christians, who by 1100 began to gain control over this Arab civilization in regions such as Toledo, Spain, and Lisbon, Portugal.

The Muslim and Jewish scholars included addendums to the original works. Thus, not only did they translate the original works from Greek to Arabic, they also completed ideas left unfinished by the ancient Greeks, thus enhancing the original works. The timing couldn’t have been better for Christian scholars, because by the mid-twelfth century they were already beginning to wonder about the relationship between God and, well, everything else. It was Aristotle who provided them with the insight they were looking for – that is, once they had all his works translated from Arabic to Latin.

There were probably several reasons Christian scholars favored Aristotle over the other ancient Greek philosophers. For one thing, he provided a very complete system of philosophy, having commented on just about everything. His writings were written in a very academic manner while still being very tractable to a general audience, having just enough common sense mixed in. Aristotle’s common sense, in part, came from the fact that he was very much an empiricist – whereas Democritus was more theoretical in thought, Aristotle was more observational; he observed nature and believed we could acquire useful information from the world in this way. Finally, Aristotle’s vision of God, although not that of a Christian God, evidently provided enough of a starting point to be integrated into a new version of Christianity of the time, thanks mostly to the likes of St. Thomas Aquinas (1225–1274).

Once successfully integrated into Christianity (and with the early European universities being tied to the Christian Church), Aristotle became the authority on just about everything, in particular science, up until about the seventeenth century. So the works of Democritus really didn’t have a chance to flourish for these reasons and a few others. Nonetheless, the seventeenth century would soon change all that as scientists sought to understand the world in a more systematic (mechanistic, or mechanical) way with the new tools available to them in the rapidly changing areas of physics and mathematics.

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