Plato and Aristotle: DefiningRules for Western Physics

Raphael, School of Athens, 1510

Totality in Turkey, 29 Mar 2006

Thales of Miletus--earliestknown eclipse prediction in585 BCE!

Views fromSide, Turkey

Last time: invention of physics Pre-pre-Socratic Western approaches

– Instrumentalism of Babylonians (patterns with no theory)– Mytho-poetic thought (unquestioned)

“With that, Posidon gathered the clouds and troubled the waters of the deep,grasping his trident in his hands; he raised all storms and all manner of winds…” (Illiad)

Pre-Socratic physis = ordered nature– Underlying reality is simple and unified– Debate, criticism, skepticism, “reason”– Relation of number to nature– Supernatural and anthropocentric explanations rejected

“Took the gods out,” I.e., natural ≠ supernatural

Last time: invention of cosmos Cosmos = sense of order (Homer)

Rowers at their oars Soldiers sleeping with arms at the ready Hera’s preparations for seduction (cosmetics) Well-regulated states like Sparta

Cosmos = world system Phythagoras “was the first to call the sum of the whole by

the name of COSMOS, because of the order which itdisplayed.” (Aetius 2.1.1)

“As our soul, which is air, maintains us, so breath and airsurround the whole COSMOS.” (Anaximenes)

Chaos = disorder, danger (sea)

Last time: why the Greeks? Egotism and cult of personality?

“Miracle of the Greek mind,” said the Greeks

Role of wealth (Marxist theory)? Greek merchants in the Mediterranean? Greek technological advances?

Literacy and alphabetic writing? Orality of pre-Socratic communities?

Sophism, competitions, pan-Hellenic games? “Classical games” at Olympia by 6c BCE

Role of politics (the Lloyd thesis)? Mercantile wealth and hoplites break aristocratic power Political debate a model for debate about physis City-state as microcosmic model for macrocosm--both

governed by laws, reason, nature (ordered regularity)

Task of today’s lecture Fate of physis in new Greek philosophy after

500 BCE Interest shifts from physics to politics, ethics

(“What is good life?”) The gods return

Long influence of Plato, Aristotle Timaeus 2d best-seller (after Bible) through 1100 Aristotle provides core curriculum for Western

universities until 1750 Defined the central questions and the acceptable

approaches to answering these questions

Context in 4th century BCE Socrates (470-399), the sophist

Shifts from physics to politics

Plato (427-347) and his Academy Philosophical community of scholars No fees, no fixed curriculum Many religious ceremonies

Aristotle (384-322) and his Lyceum Emphasized collaborative research Train political philosophers for state

Plato and “physics” Why study physics?

Practical utility Cultivation of reason

– “Allegory of the Cave” (Republic, VII)

Dualism of form/matter or mind/body Pythagorean origins (geometry is true not in drawn

diagrams but in abstract ideas of line)? Objectively real = unchanging perfect forms Solves problem of change

– Imperfect matter changes, perfect forms do not Elevates reason above empiricism

– Truth arises from philosophical reflection, not sensoryexperience, experiment or observation

Allegory of the cave (Republic, Book 7)

Sensory Experience(Body)

Eternal Forms(Soul)

Chained Prisoners

StatuesShadows

Fire

Cosmogony in the Timaeus An imagined story of origins of the cosmos

A sensible world cannot be eternal, needs creation Biological, mechanical, technological options

Contra physicists, brings back “god-talk”– Three explanatory entities

Eternal mind (demiurge or divine craftsmen) Not omnipotent, not anthropocentric like other Greek

gods (Zeus) Eternal forms Recalcitrant matter forces compromise

– Demiurge’s geometrical plan (teleology)– Empedocles’ roots (air, water, earth, fire)– Pythagoreans’ five regular solids

Plato’s geometrical atomism

Combines Pythagorean five regular solids & Empedocles’ (fl. -450)four “roots” or elements (types of unchanging matter)

Demiurge’s motive--ethics!Let us, then, state for what reason becoming and thisuniverse were framed by him who framed them. He wasgood; and in the good no jealousy in any matter can everarise. So, being without jealousy, he desired that all thingsshould come as near as possible to being like himself. Thatthis is the supremely valid principle of becoming and of theorder of the world, we shall most surely be right to acceptfrom men of understanding. Desiring, then, that all thingsshould be good and, so far as might be, nothing imperfect,the god took over all that is visible--not at rest, but indiscordant and unordered motion--and brought it fromdisorder into order, since he judged that order was inevery way the better. --Timaeus, 29d-30a

Implications of Plato’s atomism Only one type of matter (like pre-Socratics) Explains change by rearranging triangles of

air/water/fire atoms Mathematization of nature (like Pythagorus)

Geometrical forms are “real,” not matter Denies void (shape everywhere = plenum) Grounds idea of spherical cosmos in uniform,

circular motion– Creates problem of “saving phenomena”, i.e. explanation

via modeling for retrograde planets, varying brightnessof planets

– Defines rules for astronomy through 1600

Platos’s cosmos

Plato’s physics with gods “World soul” generates all motions in

cosmos (as do human souls in humanbodies)

Individual gods assigned to all planets Forms are immutable, do not cause change

Plato’s gods of order ≠ anthropocentricgods of Mount Olympus

“Nature” requires external principles oforder, i.e., forms, mind, reason

Aristotle’s critique of Plato Places reality in sensible objects

(phenomena), not invisible forms (mind) Separates sensible objects into:

– “Properties” like color, temperature, weight, etc. (likePlato’s forms)

– “Subjects” that possess properties (like Plato’s matter)– Still a dualistic natural philosophy

Reason downplayed; sensory experience andmemory stressed

Wrote 150 treatises (30 have survived), firstcomprehensive, encyclopedic philosophy inthe West

A’s 4 vocabularies of change Shifts of opposites (property-privation)

Hot to cold, wet to dry, up to down, etc.

Action of four “causes” Formal (form received by the object) Material (matter persisting through change) Moving (agent bringing about change) Final (goal or purpose served by the change)

Shifts from potential to actual Categories of being (non, potential, actual) Biological language of growth

Motion to “natural place” “Light” objects move “upward” “Heavy” objects move “downward” All natural motion caused by “unmoved mover”

Aristotle on matter

earth water

fire airhot

cold

wetdry

Aristotle’s eternal, plenumcosmos in his Physics

Celestial realm Perfect,

changeless Plenum Aetherial spheres Natural motion

=circular Unmoved mover

(God’s love) Velocities

unchanging

Terrestrial realm Imperfect, change Plenum Fire-air-earth-

water Natural vs. violent

motion Movers required

(violent motion) Velocity

proportional toforce/resistance

Apian, Cosmographia, 1540

Aristotle’s unmoved mover Stops infinite regress (a logical construct) Causes motion as final, not efficient cause (as

object of love and desire for objects moved) As pure actuality, is alive

“On such a principle, the heavens and nature depend…. Andthinking in itself is concerned with that which is best in itself …and contemplation is what is most pleasant and best. If then, godis always in that good state in which we are sometimes, this iswonderful … And life also belongs to god. For the actuality ofreason is life, and god is that actuality, and god’s essential actualityis the best and eternal life. We hold, then, that the prime mover is aliving being, eternal and most good, and so life and continuous andeternal duration belong to god. For this is god.” --Metaphysics, 1072b13ff.

“Physics” for Plato & Aristotle Differently rank reason, experience

Neither was “experimental”

Both seek coherent, consistent, comprehensiveexplanations for all of nature

Gods return as the Demiurge and Prime Mover Set key ideas for Western natural philosophy

form/matter violent/natural motion four elements potential/actual being (teleological or goal-directed change) Earth fixed at center of the cosmos