Epicurus - infinite atoms & infinite void

Question

Why does Epicurus insist that there are infinite atoms in an infinite void? Why infinite. Also, while it is clear how atomism can explain material objects, how does it explain phenomena that don't appear to be material, like ideas and emotions? How does Epicurus answer this question? What do you think of his answer?

Answer 1

Epicurus is picking up and modifying the older atomism of Democritus. His basic physical thesis is very stark:

Everything that exists is either (1) tiny bodies (atoms) or (2) empty space (void).

(Letter to Herodotus §§38–40)

From that starting point, you can unpack each part of the question.

I. Why infinite atoms in an infinite void?

Epicurus thinks finitude causes problems.

1. If atoms were finite in number, then over an infinite amount of time, they could all end up clumped together, or “used up,” and change would grind to a halt. But we clearly see ongoing formation and destruction of things. So there must be an inexhaustible supply of basic stuff: infinitely many atoms.
2. If space (void) were finite, there would have to be a “wall” or boundary somewhere. But then you can ask a Lucretian spear-type question (later made famous in Lucretius, On the Nature of Things I.958ff):
3. – If you go to the edge and throw a spear, does it go somewhere or not?
4. – If it goes somewhere, space extends beyond the supposed edge; if it doesn’t, something is blocking it, so there’s more space beyond that.
5. So it’s more rational, Epicurus thinks, simply to say: space has no outer edge; it’s infinite.
6. Infinite atoms in infinite void also explain multiple worlds.
7. With only one finite world, you might be tempted to bring in gods or design to explain why things are arranged just so. But if there are infinitely many atoms moving in an infinite space, it’s no surprise that there will be countless world-systems formed by purely natural processes. Our world is just one among indefinitely many. (Letter to Herodotus §§73–75)

So “infinite atoms in infinite void” is meant to secure (a) an inexhaustible supply of matter, (b) no arbitrary boundary of the universe, and (c) a fully naturalistic explanation of why there are worlds at all.

II. How does atomism explain ordinary material objects?

On Epicurus’ view, all macroscopic objects are just stable arrangements of atoms:

1. Atoms have basic properties: shape, size, and weight.
2. When they combine, they form compounds whose observable properties (color, texture, hardness, taste, etc.) depend on how the atoms are arranged and how they move together.

A standard Epicurean analogy (developed at length by Lucretius, On the Nature of Things II.1013–1022) is letters and words:

1. The same small set of letters, rearranged, can make wildly different words and sentences.
2. Likewise, the same basic atoms, rearranged, can make stones, trees, bodies, clouds, and so on.

So material objects are nothing over and above patterned clusters of atoms in motion.

III. What about things that don’t look material — ideas, perceptions, emotions?

Epicurus gives two key moves here:

a) The soul is material

Epicurus thinks the soul (psyche) is not immaterial, but made of extremely fine, fast-moving atoms distributed through the body, especially the chest region. (Letter to Herodotus §§63–66)

1. These soul-atoms are responsible for life, sensation, and thought.
2. When the body dies, and these atoms disperse, the person ceases to exist — which is why Epicurus argues that death is “nothing to us.”

So for Epicurus, whatever is going on when we think or feel is ultimately some very subtle motion of soul-atoms.

b) Perception and thought as atomic interactions

Epicurus also inherits the theory of eidōla (“images” or “films”) from earlier atomists:

1. Physical objects constantly shed incredibly thin atomic films that travel through the void.
2. When these films strike our sense organs, they cause perceptions — sight, hearing, etc.
3. When they interact with the soul-atoms (or when residual traces remain), they can combine with memory and association to produce mental images, daydreams, and thoughts.

Emotions, on this picture, are complex states of the soul-atoms plus our beliefs.

For example:

1. Fear of death = certain motions of soul-atoms + the belief that death is terrible or that the gods will punish us.
2. Tranquility (ataraxia) = calm, stable motions of the soul-atoms + corrected beliefs about nature and the gods.

So even though ideas and emotions don’t look material, Epicurus explains them as:

very fine-grained physical events in the soul, caused by interactions with other bodies (including eidōla) plus our stored memories and beliefs.

This is a kind of early physicalism or materialism about the mind.

IV. How does Epicurus himself defend this, and what should we think?

Epicurus’ own defense is partly empirical and partly therapeutic:

1. Empirically, he claims we never experience disembodied minds; all mental life we observe is tied to living bodies, and it weakens as the body weakens. That supports the idea that the soul is a very fine body rather than something immaterial. (Letter to Herodotus §§67–68; Lucretius III.94–135)
2. Therapeutically, if the soul is bodily and dissolves at death, then there is no surviving subject left to be punished or to suffer. This underwrites his famous argument that “death is nothing to us.” The theory of atoms and void is thus supposed to free us from fear of gods and death, and so make a life of tranquil pleasure possible.

How convincing is this?

1. Strengths:
2. It’s a remarkably modern-sounding attempt to give a fully naturalistic account of mind and world, long before modern neuroscience or physics.
3. The idea that mental states depend on the physical state of the brain/body is strongly supported by contemporary science, so in a broad sense, Epicurus was on the right track.
4. Tying philosophy of nature to ethical therapy (removing fear, promoting tranquility) is philosophically rich and historically important.
5. Weaknesses:
6. The specific physics is wrong: there are no eidōla films flying off objects in the way Epicurus imagined; to us, perception is better explained by electromagnetic waves, neural processing, etc.
7. His arguments for actual infinity of atoms and void are more intuitive than rigorous by modern standards; they don’t settle the sophisticated questions about infinity that arise in later mathematics and cosmology.
8. Reducing emotions entirely to atom-movements plus beliefs can feel incomplete; many would argue that social, historical, and cultural factors also shape what we feel and how.

So you might say:

Epicurus’ answer is not scientifically correct in detail, but philosophically it is a powerful early attempt at a consistent materialism: one world made of atoms and void, with minds and emotions understood as part of nature rather than something supernatural. Even if we reject his specific mechanisms, the general project — explaining mental life in natural terms — has been hugely influential and remains central in contemporary philosophy of mind and science.

That kind of evaluation shows you understand both the historical context and the philosophical stakes.