Thomas Aquinas
• 1225-1274
• Latin version of Aristotle corpus arrives in
Europe. Aquinas pours over it.
• Aquinas basically is responsible for the
‘rebirth of reason’
• Aquinas: God leads humans to a rational
and moral life
• Aristotle: Rationality and morality are
inherent qualities in humans.
Aquinas on Knowledge
• A) Man can know of the world only that
which he learns from experience but this
sets limits to what can be known: How
can reason and faith be reconciled.
• B) The world is intelligible to the rational
man. Whatever exists can be understood
and has a set of causes. These causes
can be known through experience and
(rational) reflection.
Roger Bacon
• There two ways of acquiring knowledge,
one through reason, the other by
experiment. Argument reaches a
conclusion and compels us to admit it, but
it neither makes us certain nor so
annihilates doubt that the mind rests calm
in the intuition of truth, unless it finds this
certitude by way of experience.
Roger Bacon
• Even if a man that has never seen fire, proves
by good reasoning that fire burns, and devours
and destroys things, nevertheless the mind of
one hearing his arguments would never be
convinced, nor would he avoid fire until he puts
his hand or some combustible thing into it in
order to prove by experiment what the argument
taught. But after the fact of combustion is
experienced, the mind is satisfied and lies calm
in the certainty of truth. Hence argument is not
enough, but experience is.
Towards Real Science
• In 1328 or earlier, Ockham, in Summa Logicae, wrote
that universals exist only in men's minds and in
language, disputing the Aristotelian principle that
such things as the final cause were self-evident or
necessary. In other words, facts could only be
correlated, not caused. Ockham's razor:
‘What can be done with fewer assumptions is done in
vain with more’.
• Does this represent a Bias?
 Jean Buridan, supported that motion was
maintained by some property of the body,
imparted when it was set in motion..
 Buridan further held that the impetus of a
body increased with the speed with
which it was set in motion, and with its
quantity of matter. Buridan anticipated
Newton by 300 years when he wrote:
...after leaving the arm of the thrower,
the projectile would be moved by an
impetus given to it by the thrower and
would continue to be moved as long as
the impetus remained stronger than the
resistance, and would be of infinite
duration were it not diminished and
corrupted by a contrary force resisting it
or by something inclining it to a contrary
motion
 This theory of impetus was also adapted
to explain circular motion of the planets
THE MERTONIANS: MEAN SPEED THEOREM –
1330S
• The law states that a body travelling at constant
velocity will cover the same distance in the same
time as an accelerated body if its velocity is half the
final speed of the accelerated body.
Distance = velocity*time = vt
Velocity = acceleration*time = at
v = at; d=vt  d =at2 (Muslim algebra)
Mertonian concept: Average velocity = (1/2) * (initial
velocity + final velocity)
• V –initial = 0  average velocity = ½*V-final
• Therefore, d = ½ at2 for object initially at rest
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Experimentally determined by
Galileo
Nicole Oresme
Circa 1350-1360 (University of Paris)
Probably the first example of what we would
consider as a modern scientist – proved the mean
speed theorem
Paris master and bishop of Lisieux who reformulated
Aristotle's doctrine of natural place in a way that
allowed for the possibility of other worlds. He taught
that the doctrine was valid providing only that heavy
bodies were located more centrally than light ones.
Since there could be many centers, there could, in
principle, be many different systems of worlds
Oresme Continued
Associated the idea of continuous change with a
coordinate system (long before Descartes)
Gave credible opposition to the idea of an unmoving
Earth:
“if a man in the heavens, moved and carried
along by their daily motion, could see the
earth distinctly..., it would appear to him that
the earth is moving in daily rotation"