Aristotle

1. 1One over many: wherever many things share one character, Platonists posit one separate Form of that character.
2. 2Self-predication: the Form is itself characterised by what it is the Form of, so the Form of Man, like individual men, is a man.
3. 3Non-identity: the Form is separate from, and not identical with, the things that share in it.
4. 4So the Form of Man together with individual men are a new many sharing one character, which by the first premise requires a further, third Man, and so on without end.
5. ∴Separate Forms lead to an infinite regress; what is predicated of many is a universal, not a separate substance, so Forms should not be posited apart from things. The premises are a modern reconstruction (Vlastos 1954, naming self-predication and non-identity): Aristotle only names the Third Man in the Metaphysics, and its fullest ancient form is Alexander's report of the lost On Ideas, with a variant in the Sophistical Refutations.

Plato objects. Plato raised the regress himself in the Parmenides, yet still held that without Forms there would be nothing for thought to fix on and discourse would be destroyed.

reductio · Metaphysics 990b15–17 · Metaphysics 1038b34–1039a3 · Metaphysics 1079a11–13 · Commentary on Aristotle's Metaphysics 84–85 Hayduck · Sophistical Refutations 178b36–179a10

Draft — not yet reviewed

1. 1Forms are posited as causes of sensible things, of their being, their coming to be and our knowledge of them.
2. 2But Forms contribute nothing to the motion or change of sensibles, and, not being in them, they contribute nothing to their being or to our knowledge of them.
3. 3To call Forms patterns in which other things participate is to use empty words and poetic metaphors.
4. 4A substance cannot exist apart from that of which it is the substance, yet Forms are said to be the substances of things and separate from them.
5. 5Even granting Forms, things do not come to be unless something moves them, and many things, such as houses and rings, come to be though Platonists posit no Forms of them.
6. ∴Separate Forms are causally idle: they explain neither the being nor the becoming of sensible things, and an adequate explanation needs moving causes and forms within things.

Plato objects. The Phaedo already separates two kinds of explanation: the "safe" answer that beautiful things are beautiful by the Beautiful, and the material conditions without which a cause could not be a cause. Forms are offered as the first kind, not as moving causes, so it is no objection that they move nothing.

dialectical · Metaphysics 991a8–b9

Draft — not yet reviewed

1. 1Motion and time are eternal.
2. 2Eternal motion requires an eternal substance that causes it.
3. 3A cause that had any potentiality might fail to act, so the cause of eternal motion must be pure actuality, without matter.
4. 4What is pure actuality cannot itself be moved; it moves other things as an object of desire and thought moves, without being moved.
5. ∴There is an eternal, unmoved, immaterial first mover, pure actuality, whose life is thought thinking itself; on it the heavens and nature depend.

Immanuel Kant objects. Kant's critique of the cosmological proof is aimed at the later argument from contingency and its tacit reliance on the ontological argument, which Aristotle's argument from motion does not make. What carries over is the first charge: the principle that everything moved has a cause has meaning only within possible experience, so it cannot take us to a first cause outside the series of appearances.

David Hume objects. When we infer a cause from its effects we may ascribe to it only what is needed to produce those effects; nothing licenses inferring a perfect, single, purely actual being.

deductive · Metaphysics 1071b3–1073a13 · Physics 258b10–260a19

Draft — not yet reviewed

1. 1Substance is said in three ways, as matter, as form, and as the compound of the two.
2. 2A natural body that has life is a substance in the sense of a compound.
3. 3The body is not what is said of a subject but the subject itself, that is, matter.
4. 4So the soul, which makes the body alive, must be substance as form, the first actuality of a natural body that has life potentially.
5. ∴The soul is the form of the living body; soul and body are one as the wax and its shape are one, and the soul (or at least most of it) is not separable from the body.

René Descartes objects. I can clearly and distinctly understand myself as a thinking thing apart from body, and what can be so understood apart can be made to exist apart by God; so the mind is a substance really distinct from the body.

Ibn Sina objects. A person created in mid-air, without sensing any part of their body, would still affirm their own existence; so the self is grasped as something other than the body. Ibn Sina presents this as an alerting (tanbih) toward the soul's being a substance in its own right, not as a demonstration, and its force is debated.

deductive · On the Soul 412a3–413a10

Draft — not yet reviewed

1. 1Suppose there was a first change.
2. 2Every change requires things capable of changing and of causing change, which must already exist.
3. 3Either those things came to be, which is itself a change before the first change, or they existed at rest, and their passing from rest to change is again a prior change.
4. 4Time cannot have a first instant, since every now is the end of a past as well as the start of a future, and there is no time without change.
5. ∴There was no first change; motion, time and the cosmos are eternal.

Thomas Aquinas objects. Neither the world's eternity nor its beginning can be demonstrated; Aristotle's arguments assume that things come to be only by natural change, which does not apply to creation from nothing. That the world began is held by faith.

Augustine of Hippo objects. The world was made with time, not in time, so there was no before in which a prior change could occur, and the question of what preceded creation has no sense.

Immanuel Kant objects. Reason can prove both that the world had a beginning and that it did not; the conflict shows the question exceeds possible experience.

philoponus objects. Aristotle's own principles refute him: an actual infinite cannot exist or be traversed, yet an eternal past means that infinitely many days and revolutions have already elapsed, and each new one adds to an infinite, with Saturn's revolutions a fraction of the sun's. So the world must have had a beginning.

al-Ghazali objects. The philosophers cannot show that an eternal will could not decide from eternity that the world begin at a definite time, and an eternal past yields infinitely many celestial revolutions that would have to be both odd and even, or one infinite a fraction of another.

reductio · Physics 250b11–252b6 · On the Heavens 279b4–283b22

Draft — not yet reviewed

1. 1We think we know a thing only when we have grasped its why, its primary cause.
2. 2"Why?" is answered in four ways: by the matter out of which a thing comes (the bronze of a statue), the form or account of what it is (the ratio 2:1 of the octave), the primary source of change (the adviser, the father), and the end for the sake of which (health, for which one walks).
3. 3So the student of nature must know all four, and should give the why in all four ways; in natural things form, mover and end often coincide.
4. 4What comes about by chance does not come about always or for the most part, but natural things, such as teeth fitted for biting, come about in this way always or for the most part.
5. 5So natural things do not come about by chance or by necessity of matter alone, but for the sake of something, though nature does not deliberate, as the art of shipbuilding would act for an end if it were in the wood.
6. ∴Full explanation in natural philosophy names four causes, matter, form, source of change and end, and nature is among the causes that act for the sake of something. Matter is a necessary condition, not the whole explanation.

René Descartes objects. Since God's purposes are beyond us, the customary search for final causes is useless in physics; natural philosophy should explain things by efficient causes alone, from the properties of extended matter.

David Hume objects. There is only one kind of cause; the scholastic distinction of efficient, formal, material, exemplary and final causes has no foundation, since causation is constant conjunction together with the mind's habitual inference.

lucretius objects. On the Nature of Things (book IV) inverts the teleological inference: eyes were not made for seeing; what is born creates its use. Organs arose first, and their functions followed.

deductive · Physics 194b16–195a3 · Physics 198a14–b9 · Physics 198b10–199b33 · Metaphysics 1013a24–b3

Draft — not yet reviewed

1. 1Natural things, such as animals, plants and the simple bodies, each have within themselves a principle of change and rest; artefacts such as a bed or a cloak have no innate impulse to change, except so far as they are made of stone or earth.
2. 2Some, like Antiphon, say a thing's nature is its primary matter: if a bed were buried and the rotting wood sent up a shoot, it would come up wood, not bed.
3. 3But a thing is said to be what it is when it is so actually rather than potentially; flesh and bone are not yet natural things until they have the form that their definition states.
4. 4Man is born from man, but bed does not come from bed; what reproduces itself is the form.
5. 5Nature in the sense of growth (phusis) is a path towards nature, and what grows tends towards its form, not back towards its matter.
6. ∴Nature is a principle of motion and rest in what has it in itself and not by accident. Both matter and form are called nature, but form has the better claim, which is why the natural philosopher must study form and the end, not only matter.

Epicurus objects. The atomist reply sides with Antiphon: atoms have only shape, weight and size, and every other quality comes and goes with their arrangement. What persists, and so what a thing really is, is its matter; form is an arrangement, not a principle.

René Descartes objects. There are no substantial forms in bodies: they explain nothing that shape, size and motion of extended matter cannot, and they make natural things seem like souls. Nature is matter moving according to laws.

dialectical · Physics 192b8–23 · Physics 193a9–b18

Draft — not yet reviewed

1. 1In every change something comes to be from something; when an unmusical man becomes musical, the man persists while the unmusical gives way to the musical.
2. 2So every change involves a subject (substrate) that persists, a form that is acquired, and a privation, the absence of that form, from which it comes.
3. 3The Eleatics argued that nothing comes to be: what comes to be must come either from what is, which already is, or from what is not, from which nothing can come.
4. 4But a thing comes to be from what is not only accidentally, in that it comes from a subject that has the privation; in itself it comes from the subject.
5. 5The same puzzle is also solved by distinguishing what a thing is potentially from what it is actually.
6. ∴Change is real and intelligible: it is the acquisition of form by a persisting subject that previously lacked it. This answers Parmenides without denying change and grounds the analysis of substances into matter and form, and potentiality and actuality.

Epicurus objects. The atomist answer to the Eleatics needs no forms or privations: nothing comes from or passes into what is not, because atoms are unchangeable, and what we call change is the rearrangement, addition and subtraction of atoms in a void.

deductive · Physics 189b30–191a22 · Physics 191a23–b34

Draft — not yet reviewed