The Work of Isaac Newton
Sets the Stage for
Rationalism:
– Isaac Newton (1642-1727) - published
Principia Mathematica (Mathematical
Principles) in 1687.
• Established the universal “laws of motion”
• Three “laws of motion” provide the mathematical
explanations of all observed physical activity
(except electricity and magnetism).
• The source of gravity is revealed to be an object’s
own mass. Therefore, the laws are also considered
to be the “law(s) of gravity.”
Newton’s influence
• The laws of motion gave humanity its first
complete (having no exceptions) set of
universal principles for exploring the
natural world.
– Third law (the most famous) states, “every
action has an equal and opposite reaction.”
• Newton also claimed to be able to see God
in his principles, and gave rise to the
belief in God as a “perfect clockmaker”
(Deism).
Age of Reason (1700-1800)
• Also known as “Age of Rationalism”
• Thanks to Newton, many philosophers
look for explanations of our human nature
within a world that is run by absolute
laws.
• “Reasoning,” or “the rational mind,” is the
first explanation to achieve widespread
popularity.
Rationalism
• Three driving principles:
• a) Rationalism emphasizes a priori
knowledge.
• b) Rationalists most often postulate an
active mind that acts upon incoming
sensory information.
• c) Rationalists emphasize deductive
arguments, using logic to demonstrate that
the premises of an argument provide
definitive grounds for the conclusion
(Aristotle’s basic assumption).
Who was Descartes?
• Son of a minor noble family
• Studied with the Jesuits at La Flèche (1604-1612),
studied logic, Aristotelian ‘Scholastic’ philosophy, some
maths
• Law degree 1616 (following his father)
• Soldier (a noble’s occupation) (1618-19)
• Peripatetic in Europe 1620-1628
• Settled in Holland 1628; pursued his studies privately,
corresponded with other philosophers (scientists) such
as Mersenne
• Died in Stockholm, 1650.
René Descartes
(1596-1650)
Major Themes
• Reconstruction of epistemology on new
foundation
• Man is a thinking thing—this is certain; animals
are mere machines
• Mind-Body Dualism: res cogitans vs res extensa
• Innate Ideas (cf. Locke!)
• Proof of Existence of God starting with human
imperfection: doubt
• Universe/nature as mechanism
Descartes’ Education
• Three defining quotes:
• “I took especially great pleasure in mathematics
because of the certainty and the evidence of its
arguments.”
• “Of philosophy I shall say only that…there is
nothing about which there is not some dispute—
and thus nothing that is not doubtful….”
• “As to the other sciences, since they derive their
principles from philosophy, I judged that one
could not have built anything solid upon
foundations having so little firmness.”
Descartes’ Thinking…
•
•
•
•
Believed in a provisional morality, a home in which
to reside while the new house is under construction.
(Similar to Popper's view of theories)
Accepts laws, religion and other external conditions
in his culture (cf. Socrates);
Wishes to know himself first (Socratic idea: “the
unexamined life is not worth living”).
Descartes’ Stoicism: “conquer myself rather than
fortune.”
Rejects Skepticism for its own sake; wants to focus
on attaining certainty.
Descartes’
Thinking…(continued)
• Doctrine of innate idea of natural laws
• Imagines an alternate, identical world according
to exactly the same physical laws: “…I here
resolved to leave all this world to their disputes
and to speak only of what would happen in a
new world were God now to create enough
matter to make it up, somewhere in imaginary
space…” (Hackett, p. 24).
Descartes’
Thinking…(continued)
•
•
•
•
•
Innate Ideas
Natural components of the mind
Possess great clarity and distinctiveness
Absolute perfection (the perfect thought)
Examples:
–
–
–
–
–
unity
infinity
perfection
the axioms of geometry
God
Descartes’
Thinking…(continued)
• Principles of philosophy were cognitive but
discovered through intuition.
• Searched for truth by engaging in intense
meditation (while lying in bed)
• He was a rationalist (stressed importance
of thought processes), a nativist (stressed
importance of innate ideas), but also a
phenomenologist (used introspection to
study the nature of intact, conscious
experience).
The Mind-Body Issue
• Descartes argued that the mind-body interaction
particular to humans takes place in the pineal
gland which produces a hormone that affects the
modulation of wake/sleep patterns and seasonal
functions. He believed the following propositions
regarding the pineal gland:
• a) The pineal gland is found only in humans.
• b) The pineal gland is richly supplied with nerves.
• c) The pineal gland can move freely from side to
side.
• The pineal gland is seat of sensory modules (see
next slide)
• Sensations do not inform the mind about
extramental things; rather, they enable the soul
to assess utility of extramental objects.
The Pineal Gland
Descartes’ Scientific
Approach
• Descartes applied his mathematical
approach to philosophy in his development
of a rational system.
• Descartes employed his mathematical
method as to push the limits of his ability
to doubt. His “method” consists of ifour
parts:
Descartes’ Scientific
Approach (continued)
• a) Never accept anything as true unless it
is clear, distinct, and immune from doubt.
• b) Divide all difficulties into as many parts
as possible.
• c) Start with the easiest and simplest
elements and then proceed to the
complex (similar to Locke).
• d) Keep complete notes and
comprehensive reviews so nothing is
omitted.
Descartes’ Fundamental
Principles
• Descartes started with Montaigne’s skepticism
and doubted. While Descartes doubted
everything, he could not doubt that he was
doubting. He maintained that because he was
doubting he was thinking, and because he was
thinking he was existing. Here he makes his
famous statement, “I think, therefore I am.”
• After establishing his own existence, he accepts
clear and distinct sense experience, and then he
can proceed to rely on his experience in his
research.
• Descartes postulated a non-extended mind that
is qualitatively different from the physical body.
Descartes’ Fundamental
Principles:
Spinoza’s Challenge
• Descartes presented qualitative distinctions between
mind and body, between sacred and secular, and
between humans and animals.
• Spinoza challenged Descartes’s dualisms, particularly
the means by which qualitatively different
substances such as mind and body interact, and
argued for a monistic pantheism; there is only one
substance, and it is God.
• Spinoza advocated double-aspect monism. Even if
humans use different languages to discuss the
mental and physical worlds, the mental and physical
are only two aspects of the same reality, God.
Spinoza challenge
• For Spinoza, the two aspects of humans
move in response to natural laws, and
there is no room for free will.
• Spinoza’s thoroughgoing monism prohibits
powers separate from God, and therefore
denies the existence of demons. In this
way, Spinoza may have helped challenge
the intellectual foundation of the
inquisition (see Chapter 9).
The Leibniz Challenge
• Gottfried Wilhelm Leibniz was a brilliant
mathematician and diplomat, and he also struggled with
Descartes’s dualism and the requirement of mind-body
interaction.
• Leibniz proposed a monadology, a system in which
indivisible units of existence(monads) moved in parallel in
a preestablished harmony without interacting. Mind and
body function like two clocks on a wall; they are in
harmony without influencing one another.
• Though monads do not interact with one each other, they
may come together in experience.
• Thus, in a storm, we are not aware of the sound of each
individual raindrop, but these petites perceptions can add
in experience to form the complex stimulus that we hear.,
a rain storm.
The Leibniz Challenge
• For Leibniz, the mind is an active force in
manipulating sensory input, and thinking
activity has its own trajectory beyond
sense data.
• Leibniz argued for uniformitarianism; he
claimed that change is gradual and takes
place over long periods of time.
• Christian von Wolff extended the work
of Leibniz and was one of the first to use
“psychology” in a publication.
Descartes and Physiology
• Descartes was interested in the problem of
movement in physical bodies. He endorsed a
hydraulic model of bodily movement; human
and animal bodies, for Descartes, are complex
machines. (Drive reduction theories?)
• Descartes argued that the ventricles of the brain
stored animal spirits, composed of very small
and fast-moving particles, and that movement
was enabled when animal spirits flowed down a
nerve pipe to the muscle, which then inflated
with animal spirits and stimulated movement.
• The flow of animal spirits was regulated by
small threads that opened valves in the
ventricles in response to an environmental
stimulus.
Descartes’ Contributions to
Modern Psychology
• Laid the foundation for stimulus-response
and behavioristic psychology
• Proposed the brain is a mediator of
behavior
• Clarified the mind-body relationship
• Arguably the father of physiological and
comparative psychology
• Paved the way for the for scientific study
of consciousness