Posts by Cassius

Yes that video sets up the issue very well thank you!

Welcome to Episode 327 of Lucretius Today. This is a podcast dedicated to the poet Lucretius, who wrote "On The Nature of Things," the most complete presentation of Epicurean philosophy left to us from the ancient world. Each week we walk you through the Epicurean texts, and we discuss how Epicurean philosophy can apply to you today. If you find the Epicurean worldview attractive, we invite you to join us in the study of Epicurus at EpicureanFriends.com, where we discuss this and all of our podcast episodes.
   
This week we start are continuing our series reviewing Cicero's "Academic Questions" from an Epicurean perspective. We are focusing first on what is referred to as Book One, which provides an overview of the issues that split Plato's Academy and gives us an overview of the philosophical issues being dealt with at the time of Epicurus. This week will focus on the ending of Section 7.

Our text will come from
Cicero - Academic Questions - Yonge We'll likely stick with Yonge primarily, but we'll also refer to the Rackam translation here:

• Cicero On Nature Of Gods Academica Loeb Rackham : Free Download, Borrow, and Streaming : Internet Archive

Quote

And they say that the parts of the world are all the things which exist in it, and which are maintained by sentient nature; in which perfect reason is placed, which is also everlasting: for that there is nothing more powerful which can be the cause of its dissolution. And this power they call the soul of the world, and also its intellect and perfect wisdom. And they call it God, a providence watching over everything subject to its dominion, and, above all, over the heavenly bodies; and, next to them, over those things on earth which concern men: which also they sometimes call necessity, because nothing can be done in a manner different from that in which it has been arranged by it in a destined (if I may so say) and inevitable continuation of eternal order. Sometimes, too, they call it fortune, because it brings about many unforeseen things, which have never been expected by us, on account of the obscurity of their causes, and our ignorance of them.

These are very relevant points Dave and I think about them all the time. Here's my current view.

Quote from DaveT

On the other hand I see progress away from the monarchical God and church appointed governments of the last 250 years. No longer do we accept conquest in the name of god's command to subjugate the earth.

I don't think I am violating the no-politics rule by observing that the world is on the brink of WW3 and I would say that a major reason is that most of the world is still in the grip of religious and philosophical absolutism of the very kind that Epicurus was fighting against.

Quote from DaveT

I think there is something to be said about a focus on the secular adaptation of Epicurean principles that have made their way into common society, into academia and medicine as well as government policies even though those principles are not often recognized as Epicurean.

Unfortunately here too I am convinced that the darker side of this overwhelms the brighter. The "secular adaptation of Epicurean principles" is largely a bastardization of what Epicurus actually taught, and is in fact being used to suppress any reemergence of his actual teachings. I'll paraphrase someone I don't particularly admire and say that the most "common secular adaptations of Epicurean principles" - by which I mean the elevation the pursuit of immediate pleasure as a tranquilizer against deeper understanding of philosophical issues which undermine the word today as they did in 300 BC - are as much the opiate of the people as any religion.

Quote from DaveT

Most PEW polling shows the decline of popular participation in religious organizations.

I think you're talking about our "first world" situation primarily in the USA. Disturbingly even here I understand the evidence shows a resurgence in religious interest, particularly Catholicism, and of course I am not seeing that as a positive development. It's interesting to consider that in Catholicism we see preserved many of the same Platonic/Stoic positions that were incorporated directly into it. The early Catholic "church fathers" understood Epicurus to be strong opposition. I do think that a lot of the turmoil in organized religion presents an opportunity for the re-emergence of a true Epicureanism, but that re-emergence isn't going to be accomplish by a superficial understanding of Epicurus as a neo-Stoic / neo-Buddhist / Humanist who is running from philosophical and social engagement to live a minimalist / ascetic life.

Quote from DaveT

On your point of searching for a way to deal with newer people, I'm guessing you mean newer to the Forum. I've heard that the way to engage with others is to ask those people, who they are in real life, why they joined, what their goals are at the Forum, and perhaps when they might have the time to participate. I think those questions can be asked tactfully, not just to new people, but perhaps they might become a part of an annual discussion among the membership.

I largely agree with you here but there is a danger that I also constantly consider:

Until people understand what Epicurus was really all about, they are tempted to focus only on the surface ethical questions such as how to experience more pleasure than pain under a conventional outlook of focusing only on stimulative pleasure. There are also those who come here fully convinced that the goal of life is "tranquility" and the last thing they want to do is to face uncomfortable deeper questions. Posts from such people give us an excellent opportunity to educate them about the full meaning of the texts, but too much emphasis on "momentary pleasures" and "relief from anxiety" without understand that "relief from anxiety" does not mean a "zero state," but pleasure in the full and true meaning of the word, is difficult to deal with given existing resources.

We need more people actively writing about Epicurus from a more educated and deeper perspective, so I think the priority has to be "educating the educators" so we can better address exactly what you are talking about with people who are just beginning to read Epicurus.

Episode 326 of the Lucretius Today Podcast is now available. This week our episode is entitled: "Who Cares About Infinite Divisibility? And Why?"

Quote from DaveT

I think it would be a better course to maximize Epicurus’ reasons for his physics and minimize the study of the details for the average student, like me.

Probably that's the cruc of the issue. There's a wide variety of people here with different backgrounds and interests, but this is primarily a forum for the promotion of Epicurean philosophy, not for philosophy generalists (not placing you in that latter category).

I am working on how to better deal with people on the newer side but as I see it the primary need in Epicurean philosophy is not that of building bridges to people of different opinions but working to develop a core team of people who like me share the conviction that Epicurus is uniquely worth rebuilding a "team" or "camp" of those who want to approach modern problems from the perspective of actual ancient Epicureans.

In most respects other than pure technology I see mostly regression from 2000 years ago, and in order to deal with that regression we need to focus on where things went wrong and how applying core Epicurean attitudes could redress those problems.

There are plenty of places on the Internet where people can discuss raw hedonic calculus from generic point of view, but almost no one bringing to bear the insights that people like Dewitt and Sedley have written about over the last 50 years.

So I will work on both but that's the explanation for where we are.

Dave, the answer to both of your questions seems to me to be pretty much the same. These things are not "totally subjective" nor are they "just brain chemistry." As the article is discussing, emergent properties like the mind's actions are not mechanically determined by atoms and void, nor are they totally subjectively under the power of the mind. Most people cannot through mental will power find buring their hands in a fire to be pleasurable - on the other hand did not the feeling of pleasure and pain work regularly across people, there would never be any regularity at all in what people find to be pleasurable or painful.

That's why this discussion is important. Epicurus is discussing the limits and boundaries of properties of atoms and the qualities that emerge from combinations of atoms. All of this directly refutes the idea that human life is either chaotic or determined supernaturally.

And in the end what we are doing is PHILOSOPHY - we are exploring a 'systematic study of nature' that allows us to have confidence that all of this is occurring naturally and without input from or direction from gods (if you're the religious type) or chaotically (if you're the nihilist type). I suspect that you are neither and that's why you think it's ok to go right to ethics, but Epicurus thought (and I do too) that the world in general is not that way, and that everyone from childhood needs to be taught a systematic approach to the way the world works that allows us to live successfully.

These are the issues we are really talking about and that Epicurus is addressing. Epicurus could care less whether we call fundamental particles atoms or protons or neurons or quarks or anything else, and I think if he were here today those who focus on that perspective are in fact lost and will never see the bigger picture until they back up and decide philosophically what "reality" really means.

Thanks for your question, Dave. It comes up frequently so I have updated the FAQ. Here's the short version:

Epicurus would be the last person to insist we cling to 2,000-year-old technical details in physics just because he said them. He was emphatically committed to observation and experience over authority — including his own. So when you say modern physics has advanced what Epicurus encouraged, I agree completely. The question is really: what specifically did Epicurus encourage in the area of physics, and why does it still matter to how we live?

Here's the crux: Epicurean physics was never really about the technical details of atoms for their own sake. It was constructed to do a specific job — to address three towering sources of human misery:

1. The fear that supernatural gods are watching us, judging us, and will punish us after death.

2. The fear that the universe is governed by Fate or Necessity, that nothing we do matters, and that we have no real agency in our own lives.

3. The view that what we see around us is not real, and that our lives and everything we value is essentially 'unreal."

Epicurus built his physics — the atoms, the void, the swerve, the emergent properties of compound things — specifically to establish that the natural world we experience is self-sufficient and self-explanatory. Nothing comes from nothing; nothing goes to nothing; the universe operates by natural processes, not divine whim or iron destiny. That framework is what allows the ethics to work. Pull out the physics, and you immediately create space for the supernatural to rush back in — which is exactly what Epicurus' rivals (Plato, the Stoics, and later the Christians) did with great success.

Now, as to the Sedley article specifically — and the question of whether Epicurus was a "reductionist" — this turns out to be very relevant to modern Epicurean life, more than it might first appear. Sedley's argument is that Epicurus was not a strict reductionist: he did not say that your feelings of pleasure and pain, your lived experience, your psychological states are "mere illusions" that dissolve into atomic physics if you look closely enough. The qualities of compound things — including the pleasure and pain we feel — are real, not eliminable, and must be understood at their own level. That is philosophically powerful ammunition against the modern dismissal of Epicurean ethics as "merely subjective" or "just brain chemistry."

So the short answer to your question "why should I care about the atoms debate if so much science has changed?" is: care not because the technical atomic details are sacred, but because the method and framework Epicurus established — natural causation, no supernatural intervention, emergent reality at the level of lived experience — is exactly what you need to build and defend a life philosophy grounded in nature. And you need confidence in a framework that establishes that your life and the things you value are truly real. The details update as science advances; the framework remains as essential as it ever was.

The full updated FAQ answer is here:

Why Should I Care About Epicurean Physics When So Much Science Has Changed in the Last 2,000 Years? - Epicureanfriends.com

www.epicureanfriends.com

Eikadistes I thought of your article in reading David Sedley's "Epicurean Anti-Reductionism," and I wanted to be sure you saw this.

I don't recall all the details of your article, but I think you'd find the concluding section of Sedley's article supportive of the argument that Epicurus should really not be considered primarily an atomist.

The following is a quotation translated by David Sedley from Epicurus' On Nature 34.21-2. It comes from Sedley's discussion of "Downward Causation" in how the mind itself can influence the atoms. There are numerous implications that can be drawn from it but to my observation it's not a well-known quote so I therefore give this its own thread. The clip comes from Sedley's "Epicurean Anti-Reductionism" page 319.

This week I would like us to take a step back from where we are in Lucretius so that David Sedley can explain the implications of the detail through which we are going about atoms and void. We've talked previously about his article "Epicurus' Refutation of Determinism" which discusses these issues, but the same questions are explored with greater detail and clarity in this article:

Thread

Article - David Sedley - 1988 - "Epicurean Anti-Reductionism"

We've referenced many times on the forum the comments about this topic made by David Sedley in his "Epicurus' Refutation of Determinism."

I don't think we previously cited - or that I knew of - an article Dr. Sedley had written directly on point:

Epicurean Anti-Reductionism - 1988 - J. Barnes, M. Mignucci (eds.), Matter and Metaphysics (Naples 1988), 295-327

Full article available here:

https://www.academia.edu/3051123/Epicurean_anti_reductionism

Summary of Main Arguments and Highlights

1. Core

…

Cassius

March 26, 2026 at 9:13 AM

We won't by any means have time to go through the full article but we'll discuss the highlights, as these will help us grasp the takeaways of the issues we're discussing each week:

Summary of Main Arguments and Highlights

1. Core Thesis: Epicureanism is Not Fully Reductionist

• Sedley’s central claim is that Epicurean philosophy, although grounded in atomism, cannot be understood as a purely reductionist system.

  • While everything is composed of atoms and void, Epicurus does not reduce all explanations to atomic properties alone.
  • Instead, Epicureanism allows for higher-level explanations that are not eliminable into micro-level physics.

  Key implication:
  Epicurus is a qualified materialist, not a strict reductionist.

  ---

2. Distinction Between Atoms and Compounds

• Sedley emphasizes a crucial distinction:

  • Atoms: possess only a few immutable properties (shape, size, weight).
  • Compound bodies: exhibit qualities that do not belong to atoms themselves.

  This aligns with Lucretius’ distinction between:

  • Coniuncta (necessary qualities)
  • Eventa (accidental qualities)

  These qualities:

  • Depend on atomic arrangements
  • But are not reducible to atomic descriptions

  ---

3. Emergent Qualities Are Real (Not Illusions)

• A central anti-reductionist point:

  • Qualities like color, heat, solidity, life, and agency are:
    • Not properties of individual atoms
    • Yet genuinely real features of compound bodies

  Sedley stresses that Epicurus:

  • Does not treat these as mere appearances or illusions
  • Instead treats them as objective, though derivative, realities

  Conclusion:
  Epicureanism supports a form of emergence—higher-level properties arise from but are not identical to lower-level constituents.

  ---

4. Explanatory Pluralism

• Sedley argues that Epicurus uses multiple levels of explanation simultaneously:

  • Micro-level: atoms and their motions
  • Macro-level: observable phenomena and qualities

  These levels are:

  • Compatible, but
  • Not interchangeable

  Thus:

  • Some explanations are best given at the level of bodies, not atoms.

  ---

5. Rejection of Eliminative Reductionism

• Epicurus rejects the idea that:

  Quote

  Quote

  Only atomic-level facts are “really real”

  Instead:

  • Observable properties retain explanatory legitimacy
  • Everyday descriptions (e.g., “fire is hot”) are philosophically valid

  This is a direct rejection of:

  • The view that higher-level properties must be eliminated in favor of physics

  ---

6. Stability and Identity of Objects

• Sedley highlights that:

  • Compound bodies have stable identities
  • These identities depend on:
    • Structural organization
    • Functional roles

  Not merely:

  • A list of atomic constituents

  Thus:

  • A thing’s identity is tied to its emergent organization, not just its atoms

  ---

7. Ethical and Psychological Implications

• This anti-reductionism is not merely physical—it extends into ethics:

  • Human experiences (pleasure, pain, fear) are:
    • Grounded in atomic processes
    • But must be understood at the level of lived experience

  Epicurus therefore:

  • Treats psychological states as real and explanatorily significant
  • Not reducible away into physics

  ---

8. Lucretius as Key Evidence

• Sedley relies heavily on On the Nature of Things to support this interpretation:

  • Lucretius explicitly distinguishes:
    • Atomic properties
    • Emergent qualities of bodies
  • He shows that:
    • Qualities arise from arrangements and interactions, not intrinsic atomic features

  ---

Overall Interpretation

• Sedley’s interpretation can be summarized as follows:

  • Epicurus is a materialist → everything is made of atoms and void
  • But also an anti-reductionist → not everything can be explained purely at the atomic level

  This results in a philosophical position that combines:

  • Ontological reduction (everything is atoms)
  • With explanatory pluralism (not everything is explained in atomic terms)

  ---

Concise Takeaway

• Quote

  Quote

  Epicurean philosophy holds that while atoms are the fundamental constituents of reality, the world we experience—including qualities, objects, and human life—must be understood at their own level and cannot be reduced away into atomic descriptions.

In this article Sedley refers several time to aetiology and ontology and discusses which aspect is primary to Epicurus on a particular point. It might help to have this explanation before reading the article (pasted from our good friends at ChatGPT):

The phrase “aetiologically rather than ontologically primary” distinguishes two different senses in which something can be considered “primary” or fundamental.

1. Aetiologically primary (causally primary)

• Aetiology means cause or explanation of origin.
• If something is aetiologically primary, it is:
  • The cause or source of something else
  • What explains how or why something comes to be

👉 In simple terms:
It comes first in the order of explanation or causation.

2. Ontologically primary (being primary)

• Ontology concerns what exists and what is fundamentally real.
• If something is ontologically primary, it is:
  • More fundamental in reality
  • What other things depend on for their existence

👉 In simple terms:
It comes first in the order of being or reality.

This topic was also discussed in a recent zoom meeting. The answer appears debatable, and I see that Sedley's article "Epicurean Anti-Reductionism" has this to say (see especially footnote 29):

Here is the translation from Demetrius Lacon cited on page 306:

There's a LOT of interest in that article. Here's a section that both interesting and "funny" as to what should probably be our love-hate relationship with Cyril Bailey:

From the Sedley Article "Epicurean Anti-Reductionism"

We've referenced many times on the forum the comments about this topic made by David Sedley in his "Epicurus' Refutation of Determinism."

I don't think we previously cited - or that I knew of - an article Dr. Sedley had written directly on point:

Epicurean Anti-Reductionism - 1988 - J. Barnes, M. Mignucci (eds.), Matter and Metaphysics (Naples 1988), 295-327

Full article available here:

Epicurean anti-reductionism

Epicurean anti-reductionism

www.academia.edu

Summary of Main Arguments and Highlights

1. Core Thesis: Epicureanism is Not Fully Reductionist

Sedley’s central claim is that Epicurean philosophy, although grounded in atomism, cannot be understood as a purely reductionist system.

• While everything is composed of atoms and void, Epicurus does not reduce all explanations to atomic properties alone.
• Instead, Epicureanism allows for higher-level explanations that are not eliminable into micro-level physics.

Key implication:
Epicurus is a qualified materialist, not a strict reductionist.

2. Distinction Between Atoms and Compounds

Sedley emphasizes a crucial distinction:

• Atoms: possess only a few immutable properties (shape, size, weight).
• Compound bodies: exhibit qualities that do not belong to atoms themselves.

This aligns with Lucretius’ distinction between:

• Coniuncta (necessary qualities)
• Eventa (accidental qualities)

These qualities:

• Depend on atomic arrangements
• But are not reducible to atomic descriptions

3. Emergent Qualities Are Real (Not Illusions)

A central anti-reductionist point:

• Qualities like color, heat, solidity, life, and agency are:
  • Not properties of individual atoms
  • Yet genuinely real features of compound bodies

Sedley stresses that Epicurus:

• Does not treat these as mere appearances or illusions
• Instead treats them as objective, though derivative, realities

Conclusion:
Epicureanism supports a form of emergence—higher-level properties arise from but are not identical to lower-level constituents.

4. Explanatory Pluralism

Sedley argues that Epicurus uses multiple levels of explanation simultaneously:

• Micro-level: atoms and their motions
• Macro-level: observable phenomena and qualities

These levels are:

• Compatible, but
• Not interchangeable

Thus:

• Some explanations are best given at the level of bodies, not atoms.

5. Rejection of Eliminative Reductionism

Epicurus rejects the idea that:

Quote

Only atomic-level facts are “really real”

Instead:

• Observable properties retain explanatory legitimacy
• Everyday descriptions (e.g., “fire is hot”) are philosophically valid

This is a direct rejection of:

• The view that higher-level properties must be eliminated in favor of physics

6. Stability and Identity of Objects

Sedley highlights that:

• Compound bodies have stable identities
• These identities depend on:
  • Structural organization
  • Functional roles

Not merely:

• A list of atomic constituents

Thus:

• A thing’s identity is tied to its emergent organization, not just its atoms

7. Ethical and Psychological Implications

This anti-reductionism is not merely physical—it extends into ethics:

• Human experiences (pleasure, pain, fear) are:
  • Grounded in atomic processes
  • But must be understood at the level of lived experience

Epicurus therefore:

• Treats psychological states as real and explanatorily significant
• Not reducible away into physics

8. Lucretius as Key Evidence

Sedley relies heavily on On the Nature of Things to support this interpretation:

• Lucretius explicitly distinguishes:
  • Atomic properties
  • Emergent qualities of bodies
• He shows that:
  • Qualities arise from arrangements and interactions, not intrinsic atomic features

Overall Interpretation

Sedley’s interpretation can be summarized as follows:

• Epicurus is a materialist → everything is made of atoms and void
• But also an anti-reductionist → not everything can be explained purely at the atomic level

This results in a philosophical position that combines:

• Ontological reduction (everything is atoms)
• With explanatory pluralism (not everything is explained in atomic terms)

Concise Takeaway

Quote

Epicurean philosophy holds that while atoms are the fundamental constituents of reality, the world we experience—including qualities, objects, and human life—must be understood at their own level and cannot be reduced away into atomic descriptions.

Among the topics we discussed in a zoom last night was what does Epicurus say about atomic size whether there a finite range of atomic sizes? The following is AI so take it only as a possible starting point.

Atomic Size (μέγεθος) in the Letter to Herodotus

What Epicurus Actually Says (§§55–56, 58–59)

Epicurus establishes two constraints on atomic size that work in opposite directions, producing a finite range:

Lower bound — atoms are not infinitely small: Atoms cannot be arbitrarily tiny because they must be composed of a minimum number of minimal parts (ἐλάχιστα). The atom is the smallest composite body — it has parts that are conceptually distinguishable as minima, even though those parts cannot exist independently. This is the famous theory of minimal parts, developed in part to answer Zeno's paradoxes of infinite divisibility. An atom of one minimum part would be a mathematical point, not a physical body.

Upper bound — atoms are not perceptible: Epicurus states explicitly that no atom is ever large enough to be seen (§55). If atoms were perceptible in size, we would observe them. We do not. Therefore their sizes must fall entirely below the threshold of perception.

The relevant sentence from §55 (paraphrased): atoms have size, shape, and weight, but no quality that perception can grasp — they cannot be seen, tasted, or touched as individual atoms.

Why a Finite Range of Sizes?

The argument runs something like this:

1. Atoms differ in size (this is required to explain why compounds differ — identical atoms could not produce variety).
2. But the variation is bounded: there is a smallest possible atom (a body with the fewest possible minimal parts, probably one or two) and a largest possible atom (still sub-perceptible).
3. Therefore the range of atomic sizes is finite in number of types, even if the number of individual atoms within each size-type is infinite.

Epicurus makes this explicit: the varieties of atomic shapes are not infinite in number, only incomprehensibly large (§42). The same logic applies to sizes. An actual infinity of size-types would create serious problems — it would allow for atoms large enough to be perceptible, which contradicts the evidence of experience.

Sedley's Analysis

Sedley (Lucretius and the Transformation of Greek Wisdom, 1998, and "Epicurean Anti-Reductionism," 1988) emphasizes that the minimal parts doctrine is Epicurus' own innovation, not found in Democritus. For Democritus, atoms could in principle be any size — Epicurus constrains this by grounding atomic structure in a discrete geometry of minima. This gives the size property a quasi-mathematical character: atomic size is not a continuous variable but a discrete one (how many minima make up this atom?).

This is philosophically significant because it means μέγεθος, unlike the emergent qualities of compounds, is intrinsic, immutable, and countable — which is precisely why it qualifies as a genuine property of atoms rather than a quality in the coniuncta/eventa sense.

Lucretius' Parallel Account

Lucretius covers this in DRN 1.599–634 (the finitude of atomic shapes) and implicitly throughout Book 2 (2.333–380 on size variation explaining sensory differences). He does not invoke the minimal parts argument as explicitly as Epicurus does, but the upper bound — atoms are always invisible — is stated clearly and used to explain why the world appears continuous even though it is granular.

Summary Table

The elegance of Epicurus' position is that both constraints are empirically motivated: one by the fact that matter is physically real (not geometric abstraction), the other by the fact that atoms are never observed directly. The finite range of μέγεθος is thus not a mathematical stipulation but a conclusion drawn from two independent observations about the nature of physical reality.

Last night in our zoom the question came up as to whether Epicurus held that atoms differ in weight. This is what AI has to say - take it for what its worth and let's discuss whether they differ in weight or not.

Atomic Weight (βάρος) in Epicurean Philosophy

Does Epicurus say atoms have different weights?

Yes — but with important qualifications. Epicurus lists weight alongside size and shape as one of the three intrinsic properties of atoms. However, the relationship between weight and the other properties is philosophically murky in ways that size is not.

The key passage is Letter to Herodotus §54: atoms differ in shape, size, and weight (βάρος). This seems straightforward. But complications arise immediately.

The Upper and Lower Bound Problem for Weight

Lower bound — every atom has some weight: This is unambiguous. Epicurus breaks decisively from Democritus here. Democritus did not attribute weight to atoms as an intrinsic property — weight for him was a relational or emergent phenomenon arising from atomic collisions and vortex motion. Epicurus insists weight is primitive and intrinsic: every atom, no matter how small, has weight, and weight is what drives the fundamental downward motion through the void (the clinamen aside). There is no weightless atom. So the lower bound is: at least some minimal quantum of weight, corresponding presumably to the smallest atom.

Upper bound — here it gets complicated: Unlike size, where Epicurus gives a clear upper bound (atoms must remain sub-perceptible), he does not give an equally crisp upper bound for weight in the Letter to Herodotus. The constraint that seems to apply is:

1. Weight must correlate at least roughly with size (a larger atom, having more minimal parts, should be heavier).
2. Since atomic size is bounded above by sub-perceptibility, atomic weight is indirectly bounded — an atom cannot be so heavy that it produces perceptible gravitational effects in isolation.
3. But Epicurus never states this explicitly for weight the way he does for size.

The Lucretius Complication

This is where things get genuinely difficult. Lucretius, in DRN 2.225–242 and 2.333–380, appears to deny that atoms differ in weight at all — or at least to deny that heavier atoms fall faster than lighter ones. His argument for the clinamen (the atomic swerve) depends on all atoms falling at the same speed in the void regardless of weight. This is the famous passage: in empty space, a feather and a lead ball fall at the same rate — only resistance (plagae) from surrounding matter creates apparent differences in falling speed.

This produces an apparent contradiction:

• Epicurus says atoms have different weights (βάρος varies).
• Lucretius says all atoms fall at the same speed.

How scholars resolve this:

Sedley (Lucretius and the Transformation of Greek Wisdom, 1998) argues these are not actually contradictory. Atoms have different quantities of weight, but in the infinite void with no resistance, the rate of fall is uniform regardless — because there is no medium to create differential drag. Weight differences matter only when atoms are in collision with other atoms, contributing to the mass and downward tendency of compound bodies. The weight of an atom is real but its effect on velocity is masked by the homogeneity of the void.

Bailey and others have argued more skeptically that Lucretius may simply be softening or misrepresenting Epicurus on this point.

Does Weight Scale with Size?

This is another contested question. The natural assumption is that a larger atom (more minimal parts) is also heavier. Epicurus seems to assume this, but he never makes it explicit. The problem is that shape also varies independently of size — a very intricately shaped atom might have more minimal parts than a compact spherical atom of the same overall dimensions. Weight, size, and shape are listed as independent variables in §54, which suggests they can vary independently of each other — a philosophically awkward result if weight is just a function of volume.

Summary of Constraints

The sources available to us are less developed than treatment of size. The minimal parts doctrine gives size a rigorous lower bound with clear mathematical structure. Weight by contrast seems to be asserted as a primitive intrinsic property largely to explain why atoms move at all — and the upper bound problem is left more implicit than resolved.

Another option:

Sedley's Routledge Encyclopedia entry (2005) states that "atoms themselves have only the primary or ineliminable features of body: size, shape and weight," and that the ground for this parsimony is the Letter to Herodotus §54–55: secondary properties are changeable by nature, whereas atoms are the enduring entities underlying change. Routledge Epicurus avoids the "reductionism" of Democritus — while everything is ultimately atoms and void, the emergent properties that arise from those combinations are not equivalent in every respect to their constituent atoms.

On the compound-body level, Lucretius distinguishes in De Rerum Natura properties that are inseparable (coniuncta, Greek συμβεβηκότα) from others that are accidental (eventa, συμπτώματα). Stanford Encyclopedia of Philosophy And crucially on the ontological status of those emergent qualities: although colors and other accidents are real, they are irreducibly different from atomic structures, and atomic structures are in no way ontologically privileged over the phenomenal level — neither level has a monopoly on truth. Routledge

Here is the main structural diagram showing the full ontological hierarchy:

Again - consider these as initial drafts that will need further revision!