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