Lecture 3 & 4: Aristotle
© D arrin Durant 2004
ARISTOTLE (384-322 B.C)
“The master of them that know” (Dante)
*** What do we see in the sky with the naked eye? ***
 Both differences and regularities
 Most see a fixed pattern rotating about a point in the sky
 Rising and setting stars, and circumpolar stars
 Longitude & Latitude
 At equator: stars rise and set vertically
 At the poles: all stars circumpolar
 Zodiac (8º either side of ecliptic (23½º angled to
equator – east/west behaving stars))
 Moon
 27-30 day cycle; changes in shape and size
 Slow, spiral, motion (westward with stars, eastward
for new moon); rises in different places in horizon
 Sun
 Westward diurnal with stars; annually eastward
 Variable Noon ‘distance’, variable shadow length
 Planets (‘wanderers’)
 Westward diurnal motion with stars; eastward normal
motion, + brief wastward retrogression
 Some vary in brightness
 General pattern is circular motion about the earth
1. The Earth is spinning?
2. The Cosmos is spinning about the Earth?
 8 to 5th century B.C: Spherical Cosmos and Earth, fixed
stars rotate about Earth in circular orbits
 Parapegmata (calendars) tradition separate from study
of the nature of heavenly bodies and their motions
 Plato (‘Myth of Er’, in the Republic; and the Timaeus)
 Multisphere model as a cosmological-moral theory
 ‘Astronomy’ as part of calendar-making and politics
Lecture 3 & 4: Aristotle
© D arrin Durant 2004
*** Eudoxus and the Two-Sphere Model ***
 Joins two traditions: calendars; nature of bodies & motions
 Eudoxus of Cnidus (390-337 B.C) . . . 341 B.C
 Basic idea: generate planetary loops out of uniformly rotating spheres (a
point on the equator of one of a pair of titled, equally rotating nested spheres = a
figure 8; rotate the figure 8 inside a 3rd spehere = a loop)
 Stars on Sphere of Fixed Stars [SFS] = E to W daily motion
 Extra nested, homocentric spheres
 Sun: on a sphere rotating, on its axis, W to E once in a
year (1º per day), inside the SFS (+ 1)
 Moon: W to E inner sphere rotating at 231/3º (+ 1)
 Planets: 4 spheres per planet
 Total = 27 spheres
 Callipus of Cyzicus (370-300 B.C)
 Sun & Moon = 5 spheres
 Planets = Jupiter & Saturn (4 each), Mercury, Venus,
Mars (5 each)
 Total = 34 spheres
 Number of spheres matched complex motions
 Saturn (29 yrs, retrogress every 378 days), Jupiter (12 yrs, retrogress
every 399 days), Mars (22 months, retrogress every 26 months), Venus and
Mercury (1 yr, retrogress every 584 and 116 days respectively); sun is faster
in winter than summer; moon wobbles along ecliptic
*** Aristotle’s Physical System ***
 Nested concentric spheres…
For the Motion of:
Number of Spheres:
Sphere of Fixed Stars 1
Total number of spheres + counterturners:
= 56
Lecture 3 & 4: Aristotle
© D arrin Durant 2004
*** Aristotle v. Plato ***
 Aristotle wanted to know why things are the way they are
 We know via the senses = philosophical knowledge
 Plato’s Theory of Forms (or Ideas):
 Eternal, transcendent realities apprehended by
thought (Forms or Ideas) v. transient phenomena of
experience (sensible particulars)
 Forms have an independent existence
 Simile of the Cave (Book VII of the Republic)
 Difference between reality and appearance
 “The one over the many” principle
 Where a plurality is known by single name
(‘woman’), there is an ideal (Form of) woman apart
from these, by which we recognize each member as a
 “The third (wo)man argument” (Parmenides)
Original plurality1 (‘woman’) + ideal = plurality2
(‘women’), ad infinitum
 Aristotle’s critique of Plato:
 Individual things are primary substances (ousia =
‘realities’), ‘group categories’ are secondary substances
 Forms have a dependent existence
 What are the most readily observable and commonsense properties of the world?
 Transformed Plato’s ‘dialectic’ (‘collection and division’)
 Aristotle’s syllogismus: “certain things being stated, something
other than what is stated follows of necessity from their being so”
E.g.: A. All men are mortal
Universal assertion
B. Socrates is a man
Minor premise
C. Therefore Socrates is a mortal Conclusion (particular)
 An objection: how do you know all men are mortal?
 Francis Bacon (1620): ‘Circularity objection’
Lecture 3 & 4: Aristotle
© D arrin Durant 2004
 Aristotle’s attitude to “experience” . . .
 Perception
We perceive…
…the same thing = familiarity = Experience
countless times…
 Thus: to have knowledge based on sensory experience is to
be familiar with [behaviours & properties] and to assume
your audience is familiar with [those behaviours & properties]
 What happens if something is not ‘familiar’ to you?
 Explain what is already known or make new discoveries?
*** Survival Guide to Aristotle ***
 Doctrine of Natural Place
 ‘Natural’ motion/change (internal and teleological –
towards a natural place) versus ‘unnatural’ (away from
natural place - external, ‘forced’ or ‘violent’)
 Terrestrial/Celestial distinction
 Terrestrial = corruption and change
 Celestial = perfection and eternity
 Astrology makes sense
 All motion requires a mover
 Doctrine of substantial forms, or ‘real qualities’
 Internal causation
 Locates attributes within bodies
 Objects (natural or social) activated from inside
 Teleology
 4 causes
Lecture 3 & 4: Aristotle
© D arrin Durant 2004
*** Geometric Centre to Outermost Sphere ***
Celestial Region
Lunar Sphere
Table of Opposites
Cold & Dry = earth
Cold & Wet = water
Hot & Wet = air
Hot & Dry = fire
Lecture 3 & 4: Aristotle
© D arrin Durant 2004
*** The
Terrestrial Realm ***
 No beginning (an eternal cosmos)
 Prime Matter
changed by
Pairs of Contraries
 All Bodies = a mixture of Form & Matter
Form is the mover; Matter is moved
1. Substantial
2. Qualitative
3. Change of Quantity
4. Change of Place
1. Substantial change = generation and corruption (terrestrial)
 One Form replaced by its contrary
 Actualization = Contrary in Privation (potentiality)
 Parmenides’ objection to change: ‘heat has become
coldness’ violates law of non-contradiction.
Solves Parmenidean problem of change . . .
 “This hot thing has become cold”
 Contrary left the substance and replaced by
4. Change of Place = motion (Doctrine of Natural Place)
 In the Sublunar Realm
 Each nested sphere as the natural place of an element
 Mixed bodies in their natural place Mixed bodies
 In the Celestial Realm
 A Plenum, not a Void (non-differentiated places = no
natural places to be)
 ‘Place’ defined by external container
 There cannot be an infinite cosmos (again, no natural
places causes problems)
Lecture 3 & 4: Aristotle
© D arrin Durant 2004
*** Natural versus Violent Motion ***
Motion I (Sublunar)
Natural Motion
Experience teaches: bodies
move to their natural place
Absolute heaviness &
lightness, not relativistic
Every event has a cause (NOT
simply “it moves because it is
natural to move”)
Essential natures, not
Quantitative relations
Violent Motion
Away from the natural place
Medium as both motive power
and resistance
Vacuum (void) is impossible,
because it would imply infinite
speed or instantaneous motion
No “V  F/R” (just ‘time’ and
‘distance’, not ‘velocity’)
Motion II (Celestial)
 Different kinds of motion can be explained by the internal
make-up of the Bodies in each realm
 The 5th element: Ether (perfect, immutable)
Terrestrial Elements
Natural motion = rectilinear
Elements & mixtures in a
continual state of flux
Contrary qualities =
Substantial change
Rectilinear motion due to
presence of contrary qualities
of lightness and heaviness
Celestial Ether
Natural motion = circular
Ether suffers no change
(except for ‘place’)
No contrary qualities, so no
substantial change
Without lightness and
heaviness, rectilinear motion
cannot occur
Lecture 3 & 4: Aristotle
© D arrin Durant 2004
*** The Celestial Realm ***
 Is ether matter?
 If ether is perfect, then was it homogeneous?
 Homogeneity = non-differentiated
 In the heavens, bodies already in their natural place
 Why visible differences?
 What is the nature of ‘empty space’?: Invisible, ethereal
spheres, but also real and physical
Cause of Orb motion?
External “Intelligences”
Internal Principle
By virtue of its own nature
Unmoved Movers (immaterial)
Produce motion by being ‘loved’
 Problems?
The Prime Mover
- Not kinesis, but energeia in
the form of nous; no divine
- Perfection as goal
1. The terrestrial body problem
2. The planetary influence problem
*** Aristotle & Internal Causation ***
 Heavy bodies falling
 The possibility of other worlds
 The doctrine of the natural slave
 The social instinct

Lec 3 & 4 Aristotle