Aristotle (384 BC - 322 BC)
Appeared in: Lecture 1,3.
Greek philosopher usually upheld as one of the greatest philosophers
of all times. Aristotle studied at the Academy, but disagreed with
Plato
, feeling that one could obtain knowledge about the natural world. He distinguished
between two types of philosophers: the physiologoi (natural philosophers)
who study nature (e.g.
Thales
, Anaximander
, and
Anaximenes
) and the theologoi who used gods and myths (e.g.
Homer
and Hesiod
). Aristotle believed that there exists a "golden mean," or desirable middle
ground between any two extremes. He founded his own school in Athens called
the Lyceum (or "peripatetic school," since Aristotle used to lecture
while walking) which emphasized natural philosophy. Aristotle's lectures
were compiled into 150 volumes including Physics,Metaphysics,
and De Caelo et Mundo (On the Heavens and Earth).
Aristotle philosophized on virtually every other subject. He classified
animals in a "Scala Naturae" or "Chain of Being" which consisted of God, man,
mammals, oviparous with perfect eggs (e.g., birds), oviparous with non-perfect
eggs (e.g., fish), insects, plants, and non-living matter. He considered
each link in the chain as a "species." He also made extensive taxonomic studies
of more than 500 animal species, dissecting many of them. The observations
he published in Generation of Animals and Historia Animalum (Investigation
of Animals) were meticulous, and his classification scheme conspicuously
modern, departing from the prior Greek practices of using categories such
as with feet/footless and winged/wingless. Aristotle achieved such a feat
in biology by making use of the same principles of logic (whose systematic
study he was the founder of) that he applied in his physical investigations.
He did not, however, make a real classification system for plants.
In De Caelo, a work on the heavens, Aristotle accepted the heavenly
spheres of
Eudoxus
, thought the
Earth
to be spherical, and imagined a perfectly spherical unchanging universe
centered on the
Earth
.
In trying to make a mechanical model of the crystalline spheres, he was
forced to introduce "reacting spheres." His model, however, still did not
account for variations in the planets' brightnesses. Aristotle suggested
a tetrad of elements: earth (solid), fire (energy), water (liquid), and air
(gas). Aristotle believed each element could be hot, wet, dry, or cold.
He believed earth and heaven to be subject to two different sets of laws.
Terrestrial dynamics consisted of natural (straight line, vertical, discontinuous,
towards natural place, speed proportional to weight over density) and forced
(discontinuous, towards natural place, speed proportional to force over weight)
motion. Celestial dynamics was always natural, circular, and continuous.
He also rejected the atomic theories of
Democritus
.
In his works, he examined the opinions of earlier thinkers. He believed
that all events have material (object which is changed), formal (properties
of the object which is changed), efficient (agent responsible for change),
and final (reason for change) causes. In the twelfth and thirteenth centuries
A. D., Aristotle's works came to be accepted as absolute truths, a fact
which served to effectively stifle original and experiment-based scientific
progress for centuries.
For more information:
Plato picture taken from
Eric's Treasure Troves
.
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