Aristotle’s anti‑atomism is spread across several works (especially Physics, On Generation and Corruption, On the Heavens, Meteorology), and it rests on a fairly systematic package of arguments. In modern terms, he attacks atomism on logical, physical, and ontological grounds, and builds an alternative where the world is made of continuous, qualitative bodies rather than indivisible atoms in void.

Below is a structured reconstruction of how he argues for continuity over atoms.

1. Starting point: against empty space and discrete building blocks

Atomists (Leucippus, Democritus) claimed:

• Reality = atoms in void;

• Atoms are indivisible, uncuttable, no internal parts;

• Void is empty space in which atoms move and combine.

Aristotle’s first move is to reject the void:

1. In Physics IV, he argues that void as “place without body” is incoherent:

• If void is “nothing”, it has no properties; but to do physical work (allow motion) it would need properties (e.g. dimensions).

• If bodies can exist in a void without resistance, motion becomes unbounded or undefined (e.g. no determinate velocity).

2. He also argues that natural motion (tending up or down) is explained by the inner nature of bodies and the structure of the cosmos, not by mechanical impacts in empty space.

Once void is rejected, the atomist picture of “little hard things flying in nothingness” loses its physical basis. For Aristotle, no void ⇒ no discrete corpuscles separated by absolute gaps. Matter is full and continuous.

2. Continuity as primitive: line, surface, body

In Physics V–VI and related passages, Aristotle gives a definition of continuity and uses it as a basic concept:

• A continuous entity is one whose parts:

• are not merely adjacent,

• but share a common boundary and can be divided again and again without ever reaching ultimate indivisible points.

He argues:

1. Geometrical continuity:

• A line is not made of points as atoms; points are limits, not parts.

• If it were composed of indivisible points, adding or subtracting one point would change nothing in length, making length unintelligible.

• Thus length, area, volume are fundamentally continuous, not discrete aggregates.

2. Physical continuity parallels geometrical continuity:

• A body occupies a continuous volume.

• If it were built from indivisible minima, all questions about density, rarefaction, growth, mixture, etc. would be distorted: you would always end up in “all or nothing” steps.

So from mathematics upward, he treats continuity as ontologically basic, and “point” or “indivisible” as derivative notions (limits of division, not building blocks).

3. The argument from change, growth, and mixture

In On Generation and Corruption I–II, Aristotle’s strongest anti‑atomist arguments come from analyzing change:

3.1 Substantial change vs. mere rearrangement

Atomists say:

• Nothing ever truly comes into being or perishes; only atoms rearrange.

• “Generation” is just aggregation; “corruption” is disaggregation.

Aristotle replies:

1. Qualitative change (hot to cold, sweet to bitter, etc.) cannot be reduced to mere rearrangements of unchanging, quality‑less atoms.

2. More importantly, what we call generation of a new substance (e.g. water turning into air, flesh coming from food) involves:

• the coming‑to‑be of a new form,

• not just a new pattern of the same inert pieces.

Therefore, any theory that only allows rearrangement of immutable micro‑components in a void fails to account for the ontological depth of change we actually see.

3.2 Growth and diminution

• Living beings grow by assimilation of food: the added matter becomes one continuous body with the original.

• If body were truly made of fixed, indivisible units, you couldn’t have this kind of smooth increase in magnitude and continuity—only jumps in discrete units.

Aristotle uses this to argue that matter must be:

• infinitely divisible in principle (you can always divide further),

• and continuous, allowing true fusion and assimilation.

3.3 Mixture: “all through all”

Atomists: mixture is just juxtaposition of tiny particles.
Aristotle: real mixture means each ingredient is present throughout the mixture in a genuine sense (his notion of all‑through‑all).

Example:

• In a genuine solution, it’s not that big chunks of A and B sit separately; rather, at any location you have some structured presence of both (in his qualitative vocabulary, not modern chemistry’s).

If bodies were made of absolutely indivisible atoms, mixture would always bottom out at “here only A, there only B” at the fine scale.
But our phenomenology of mixing (including chemical processes, in his terms) suggests a continuous transformation, not a mosaic of untouched atoms.

Hence, mixture again pushes him toward a continuist, qualitative conception of matter.

4. The argument from qualitative opposites and the four elements

Aristotle reconstructs “elements” differently from atomists:

• Basic elements = earth, water, air, fire, defined by contraries:

• hot/cold, dry/moist.

Elements:

• are continuously transformable into one another by changing these qualities;

• share a common underlying prime matter (hulē), which itself is not a set of little granules but an underlying capacity for forms.

If the world were made of rigid indivisible atoms differing only in shape and size, then:

• you could not naturally explain how one element becomes another (e.g. water → steam) except by arbitrary rearrangement;

• yet the very continuity of natural transformations suggests a continuous substratum that can smoothly take on new qualitative forms.

So: instead of atoms + void, he posits:

• prime matter (pure potentiality, continuous)

• structured by forms (qualitative patterns),

• yielding continuous elemental bodies.

5. The “infinite divisibility” argument

In Physics VI, Aristotle explicitly rejects the idea of a smallest indivisible body:

1. Any magnitude, if real and extended, can be conceptually divided.

2. To say “there is a length that cannot be further divided” would imply:

• a contradiction with the nature of extended magnitude;

• or that length consists of non‑lengths (points) somehow glued together.

This is parallel to his geometric argument:
just as a line cannot be composed of dimensionless points, a body cannot be composed of non‑divisible mini‑bodies. Any body, to be a body, must be continuous and divisible in principle.

For Aristotle, indivisible = not body. So “atom” as a true physical indivisible runs against his definitions.

6. Motion and causality in a plenum

Against “atoms in void” moving by mechanical impacts, Aristotle insists:

• The cosmos is a plenum—completely filled with continuous bodies.

• Motion is explained by:

• inner natures (natural places),

• and contact transmission through the medium,

• not by bodies flying freely through emptiness.

If the world is a continuous plenum:

• any motion here displaces something else there,

• there is no “jumping through nothing”.
  This picture is coherent only if matter is continuous rather than sparse points separated by void.

7. How this contrasts with atomism, in his own logic

Putting it together, Aristotle sees atomism as failing on multiple fronts:

1. Logical / geometrical:

• building continuum from indivisible “points/bodies” makes extension paradoxical.

2. Physical / dynamical:

• atoms + void cannot produce his observed continuous phenomena of growth, alteration, mixture, and inherent tendencies (natural places).

3. Ontological:

• mere rearrangement of invariant atoms cannot account for genuine coming‑to‑be and perishing of substances, only for kinematic reshuffling.

So instead he defends a world of:

• continuous, infinitely divisible matter (in principle),

• structured by forms (qualitative patterns and potentials),

• with no need for underlying indivisible corpuscles or absolute void.

8. Summary

Aristotle rejects atomism not by empirical data in the modern sense, but by a tightly interlocking set of arguments about continuity, change, and ontology. For him, geometrical magnitudes and physical bodies are essentially continuous: a line is not composed of points, and a body is not composed of indivisible mini‑bodies. Points and indivisibles are limits of division, not building blocks. Once void is denied, the picture of hard atoms moving in empty space collapses. Instead, a real physical theory must explain substantial change, growth, and mixture as continuous transformations of qualitative bodies, grounded in prime matter and form. On this view, what exists is not an atomic mosaic but continuous elements—earth, water, air, and fire—capable of interconversion through changes of qualities; the world is a plenum in which motion and causation propagate through a continuous medium, not across gaps of absolute emptiness.