quiz
The first philosopher was
The Greeks were an insular people without
much contact with other peoples
* Thales of Miletus
* Anaxagoras
* Aristotle
* Jean Paul Sartre
Thales
Pythagoras believed the Earth
was spherical because
* he measured it to be
* he believed it to be ordained by the gods
* he thought the sphere was the most
perfect shape
perfect shape
* true
* false
false
The Greeks had the ability to
measure the size of the Earth
* true
* false
true
quiz
The cosmogony of Anaxagoras
assumed that the universe was
driven by
* chaos
* the vortex
Nous
* Nous
* the Prime Mover
* the Demiurge
Empedocles invented
* the three elements
* the four elements
* the fifth element
* atoms
four elements
* the void
Democritus believed in
* the impossibility of motion
* atoms and the void
* the continuity of nature
atoms and the void
Plato
- accepted Pythagorean reincarnation:
the creator made one soul for every
star, to which a virtuous man ascended
after death (immoral men were reborn
as women)
Plato (left)
(c 425 BC – 348 BC)
Demiurge = craftsman
- rejected materialism -- the world has a
purpose and plan. The universe is the
work of the Demiurge, who is godlike
but not God, as he (it?) must work with
the universe as it is.
Plato
- the world is an animal, containing
within it all other animals
Plato (left)
(c 425 BC – 348 BC)
- Plato merged Empedocles and
Democritus: everything is made up of
four types of atoms. These were mapped
to the Platonic solids (the fifth was given
the obscure job of “delineating the
universe”).
Plato
- the world being vulgar, cannot be
permanent, and so must have been
created by the Demiurge
Plato (left)
(c 425 BC – 348 BC)
- Plato challenged the astronomers to
come up with a quantitative
(mathematical) model of the solar
system
Eudoxus and the Solar System
- takes up Plato’s challenge
- not easy!
Eudoxus of Cnidus
(c. 408 BC -- c. 355 BC)
Eudoxus and the Solar System
Mars goes around the
ecliptic in 687 days
Eudoxus and the Solar System
retrograde motion
Here are the positions that the planet Mars takes on successive nights in the late Spring. (The
dash represents the path of the sun through the same region during the same season, as registered
(for instance) at the moment just after sunset when the stars become visible).
Eudoxus and the Solar System
‘heavenly empire
inhabited by god and all
the elected’
Offsetting the axes allowed
for more complicated motion.
A third sphere was added for
the sun and moon, another
for the rest of the planets,
and one for the stars, making
a total of 27 spheres.
The simplest model
attached the planets to
spheres centered on the
Earth. Eudoxus improved
this by putting the
planets on smaller
spheres to allow for
retrograde motion.
Eudoxus and the Solar System
‘heavenly empire
inhabited by god and all
the elected’
Offsetting the axes allowed
for more complicated motion.
A third sphere was added for
the sun and moon, another
for the rest of the planets,
and one for the stars, making
a total of 27 spheres.
The simplest model
attached the planets to
spheres centered on the
Earth. Eudoxus improved
this by putting the
planets on smaller
spheres to allow for
retrograde motion.
Eudoxus and the Solar System
Aristotle
- student of Plato, teacher of Alexander
- perhaps the most important thinker of
all time
“[It
would be] two thousand years before the world
produced any philosopher who could be regarded
as approximately his equal.” --Russell
Aristotle (right)
(384 BC -- 322 BC)
"Almost every serious intellectual advance has had to begin
with an attack on some Aristotelian doctrine” -- Russell
"It is doubtful whether any human being has ever known as
much as he did" -- Magee
Aristotle
- adapted the Eudoxian solar system,
improving its accuracy by going to 55
spheres.
Aristotle (right)
(384 BC -- 322 BC)
- everything below the lunar sphere was
made of the four elements. Everything
beyond was made of the “fifth
element” (hence the word
`quintessential’), which is immutable.
- thus Aristotle had to associate
shooting stars and comets (along with
rainbows and clouds) with the sublunar
realm.
Aristotle
- adopted the Platonic idea that nature
consists of matter and form: matter is the
base material of all substance; form gives
matter unity, turning it from potentiality
to actuality
Aristotle (right)
(384 BC -- 322 BC)
- Aristotle gave form the practical job of
supplying characteristics such as
hardness, color, and weight to matter.
- this model is called hylomorphism, and
came to underpin transubstantiation
Aristotle
- every motion required a mover, tracing
back leads to the idea of the Unmoved
Mover
Aristotle (right)
(384 BC -- 322 BC)
- Q: how does an arrow move after it
has left the bowstring?
A: air swirls behind it and pushes it
forward.
Aristotle
- attempted some mathematization:
ex ‘the speed of falling bodies is in
proportion to their weight’
Aristotle (right)
(384 BC -- 322 BC)
Aristotle
- attempted some mathematization:
ex ‘the speed of falling bodies is in
proportion to their weight’
Aristotle (right)
Why didn’t he bother to test his idea?
(384 BC -- 322 BC)
“Did you ever reach [truth] with any
bodily sense? – and I speak not of
these alone, but of absolute
greatness, and health, and strength,
and, in short, of the reality or true
nature of everything.” -- Plato
Aristotle
- attempted some mathematization:
ex ‘the speed of falling bodies is in
proportion to their weight’
Aristotle (right)
(384 BC -- 322 BC)
Straton of Lamsacus
thought otherwise, as
falling water breaks
into drops -- indicating
acceleration.
Aristotle
Aristotle (right)
(384 BC -- 322 BC)
- a prediction of Aristotle’s model of the
elements: water and earth fall to their
‘natural’ place at the center, making the
Earth. Air and fire rise to their natural
place, away from the Earth. But there is
air on the Earth so the air must be
prevented from floating away. Thus the
universe must be finite. Also, there must
be a fifth element keeping the Earth and
air centered in the universe.
the ‘quintessence’