23. Democritus, Atomism, and the Problem of Change

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Lecture Notes

Main Topics #

Democritus’s Atomistic Solution #

• Democritus inherited from earlier atomists the assumption that change and motion require fundamental, indivisible units
• He proposed that all reality consists of two things: atoms (ἄτομα) and the void (τὸ κενόν)
• The atoms are eternal, unchangeable, and infinite in number; the void is the empty space necessary for motion
• This theory attempts to reconcile the Parmenidean challenge (that genuine change is impossible) with the observable fact of motion

The Thought Experiment on Divisibility #

• Democritus performed a thought experiment (which Aristotle attributes to the atomists generally) to justify the necessity of atoms
• Imagine bodies cut in every way they could possibly be cut
• Two logical conclusions follow: (1) something must remain uncut (for you cannot cut something into nothing), and (2) what remains uncut must be uncuttable
• These uncuttable residues are the atoms—the fundamental constituents of all material things
• The etymology of ἄτομος: the prefix ἀ- (negative) + τέμνειν (to cut) = uncuttable, though the term can also mean simply “uncut”

Atoms and the Void #

• Democritus acknowledges that the void must exist (what is not) in order for motion to occur
• Without the void, all things would be packed together like sardines in a can, making motion impossible
• This appears to contradict Parmenidean logic (that what is not cannot be), but Democritus insists: being must be, and nonbeing (the void) must be as well
• Aristotle’s alternative: motion can occur without the void through a kind of circular displacement, where one thing moves into the space vacated by another

Sense Qualities as Convention #

• Democritus claims that sense qualities (sweet, bitter, warm, cold, color) exist only “by convention” (νόμῳ), not by nature (φύσει)
• This doctrine reflects the influence of mathematical science, which deals with quantities and figures but not with sensible qualities
• A fragment preserved by Aristotle presents a dialogue between reason and the senses, where reason attempts to convince the senses that their perceived qualities are not real
• The senses reply: “Our overthrow is your overthrow”—implying that if sensory perception is invalid, reason itself loses its foundation

The Problem of Sense Qualities in Modern Physics #

• Schrödinger cites Democritus’s fragment and observes a parallel in modern physics: the scientific picture of the world contains no greenness, redness, or other sense qualities
• Yet all scientific instruments are marked in black and red, and scientists must read these visual markings to obtain data
• The paradox: the entire edifice of modern science depends upon sense qualities that do not appear in the scientific picture of the world
• Similarly, observations that test relativity theory and quantum theory are made using Newtonian physics, yet the numerical results cannot be ordered by Newtonian physics alone—they require relativity or quantum theory to interpret
• This creates a strange circularity: you cannot get to the new order without going through the old framework, yet the old framework cannot account for the new results

The Ambiguity in Democritus’s Atomism #

• Aristotle sometimes represents atoms as very small but having size, shape, and figure
• In other texts, Aristotle suggests Democritus spoke of atoms as points (ἀτόμων σημεῖα)
• This ambiguity may reflect Democritus’s hesitation between mathematical and natural-philosophical language
• In mathematics (geometry), a point is the only uncuttable unit; in natural philosophy, an atom is something that resists being cut but retains some minimal extension

Modern Physics and Atomic Nomenclature #

• Heisenberg points out that modern physicists misuse Democritus’s terminology by calling subatomic particles “atoms”
• Democritus meant by “atoms” what cannot be cut by any means; modern chemists first applied the term to what cannot be cut chemically, then to what cannot be cut by ordinary chemical means
• When other means of breaking apart what was called an “atom” were discovered, scientists should have abandoned the term, but kept using it out of habit
• The term “elementary particles” or fundamental constituents would be more accurate for modern physics
• Names as markers of ignorance: names like “proton” (πρῶτος = first) mark our state of knowledge at a given stage; if quarks or smaller constituents exist, the name “proton” becomes a misnomer

Key Arguments #

The Necessity of Atoms #

1. Change and motion require something unchangeable as their basis
2. If bodies could be divided infinitely, there would be no final constituents, and all would be packed together
3. Therefore, indivisible units (atoms) must exist
4. These atoms are eternal and unchangeable; all apparent change is merely rearrangement of atoms

The Problem of the Void #

1. Motion requires empty space into which things can move
2. Parmenides denies that what-is-not can exist
3. Democritus accepts the paradox: nonbeing (the void) must be as well as being (atoms)
4. Aristotle rejects this by showing that motion can occur through spatial displacement without requiring a true void

The Epistemological Problem of Sense Qualities #

1. Sense qualities are not real; only atoms and the void are real
2. Yet all human knowledge begins with the senses
3. The senses respond: if we are deceived, then reason (which depends on us) is also deceived
4. Modern science exemplifies this paradox: it excludes sense qualities from its theoretical picture but depends upon reading sensible markings on instruments

Important Definitions #

Ἄτομος (Atomos) #

• Literal meaning: uncuttable (ἀ- = negative prefix; τέμνειν = to cut)
• In Democritus: that which cannot be divided further, either in thought or in fact
• Modern misuse: applied to chemical units that can in fact be divided subatomically
• Proper referent in modern physics: elementary particles, or whatever is fundamentally indivisible at a given level of analysis

Τὸ κενόν (To kenon) #

• The void, empty space, or nonbeing
• Necessary for motion to occur
• Appears to contradict Parmenidean metaphysics (that what-is-not cannot be)
• Democritus’s resolution: what-is-not must exist precisely as the condition for motion

Νόμῳ (Nomōi) #

• By convention, by custom, or by human stipulation
• Used by Democritus to characterize sense qualities as subjective rather than objective features of reality
• In contrast to φύσει (physei) = by nature

Examples & Illustrations #

The Thought Experiment of Infinite Division #

• Begin with a body and cut it in every possible way
• Result: you cannot cut something into absolute nothingness; something must remain
• What remains uncut must be uncuttable by nature
• These uncuttables are the atoms that compose all material reality

The Sardines in a Can #

• Berquist uses this vivid image to illustrate why the void is necessary
• Without empty space, all atoms would be packed together with no room to move
• Motion would be impossible, contradicting observable reality

Scientific Instruments and Sense Qualities #

• Laboratory instruments display black markings and red markings
• Scientists read these visual markings to obtain empirical data
• Yet blackness and redness do not appear in the mathematical description of reality (no “greenness of green” or “redness of red”)
• The entire scientific enterprise thus depends on qualities it denies as real

Newtonian Physics as the Foundation for Modern Physics #

• Observations testing relativity theory and quantum theory are made using Newtonian concepts and assumptions
• Yet Newtonian physics cannot order or interpret the numerical results
• Modern theories (relativity, quantum mechanics) reveal a different order in nature than Newtonian physics allows
• But you cannot access that new order except through Newtonian observation
• This creates a strange dependence of the new on the old, while the old is superseded by the new

Questions Addressed #

How can Democritus explain change and motion without violating Parmenides’s principle that what-is-not cannot be? #

• Answer: By positing two realities—atoms (what-is) and the void (what-is-not). Both must exist; motion requires empty space.

What justifies the belief that indivisible units (atoms) must exist? #

• Answer: The thought experiment shows that infinite divisibility is impossible; something must remain uncut, and that uncut remainder must be uncuttable.

Why does Democritus deny that sense qualities are real? #

• Answer: Mathematical science, which he takes as the model for understanding nature, contains no sense qualities. What cannot be mathematized cannot be fundamental to reality.

How do modern physicists misuse Democritus’s terminology? #

• Answer: They call chemical units “atoms” even though these can be divided into smaller constituents. True atoms in Democritus’s sense are the ultimate, truly indivisible units, not chemical atoms.

Why is there a paradox in modern physics regarding sense qualities? #

• Answer: The scientific worldview excludes sensible qualities from its theoretical framework, yet empirical science entirely depends on reading visual (sensible) markings on instruments to generate data.

Notable Quotes #

“Sweet exists by custom, the bitter by custom, the warm by custom, the cold by custom, color by custom. But nevertheless, there’s another fragment of Democritus… where he has a little dialogue between the senses and reason… the senses’ reply to reason: our overthrow is your overthrow.” — Berquist, on Democritus

“In modern physics, there’s no greenness of green or redness of red, none of those sense qualities… But when we read our instruments in the lab, we have to… have the black marking and the red marking… So the whole scientific picture of the world depends upon something that doesn’t appear in the scientific picture of the world.” — Schrödinger, cited by Berquist

“Don’t be so stupid as to compare what we call an atom with what he [Democritus] calls an atom.” — Heisenberg, on the misuse of atomic terminology

“These names in a way mark our what ignorance at a certain stage.” — Berquist, on why scientific terminology changes as knowledge advances