2. Rationalism
• Reason—if it follows the right method—can
reveal all the deeper truths about the
universe (or at least all the truths worth
knowing)
• We can know essential truths through the
power of pure reason
• Reason can reveal absolute universal
certainties
• Anything less than fixed certainty does not
qualify as genuine truth
3. Can Pure Reason Lead Us to Truth?
• Rationalists answer in one of three ways:
– “Knowledge” based on observations isn’t real
knowledge at all.
– Observational knowledge as is a “lower form”
of knowledge: a type of knowledge that is
distinctly inferior to the knowledge gained by
pure reason.
– The resources of pure reason—unaided by
sensory observation—will eventually unlock
the deep structure of the universe.
4. Isaac Newton
• Drawing on the work of
Copernicus, Galileo, and Kepler, Newton
devised simple laws of motion that closed
the divide between physics and astronomy.
• Newton used careful empirical observation
in establishing his principles of motion.
– Showed how observations could be part of a
mathematical system of basic principles of all
motion, both on earth and in the heavens.
5. Results of Newton’s System
• Physics and astronomy were joined in one
scientific system
– Led to the belief that ultimately all scientific
knowledge might be unified into one great system
through allegiance to a common scientific method
• Mathematics and empirical observation did
not have to occupy opposing realms but could
exist cooperatively
• We might use these methods to discover
truths about not only astronomy and physics
but also biology, psychology, ethics, politics
6. Empiricism
• Pure reason might give us truths of
mathematics and geometry; learning the
truth about the world around us also
requires that we use the evidence of our
senses.
• To gain knowledge, we must:
– Make empirical observations
– Run experiments.
7. John Locke
• 1689: Published his empiricist
manifesto, Essay Concerning Human
Understanding
– Seen as the clearest direct empiricist challenge to
Descartes’ rationalism
• Argued that we cannot avoid starting with
sensory input
– All our ideas must ultimately come from
experience
7
8. Innate vs. Learned Structures of
Language
• Chomsky (1965): Language is too complex
for children to learn in just a few years;
we must be born with an innate template
for language development
• Skinner (1966): We should not fall back on
claims of innate ideas or innate theories
until we have thoroughly examined the
possibilities of acquiring language through
learned experience
9. David Hume
• Reason and experience may tell us how to
accomplish our goals and what paths are
most likely to lead us to our desired
destination.
• Reason can give us no answers as to what
goals are worthy of pursuit.
10. David Hume
• There are profound gaps in our
understanding of the basic nature of the
world.
– We speak confidently of knowing causes, but
all we really observe is one event regularly
followed by another.
– We rely on the principle that the future will
be like the past, using the principle of
induction; this is “begging the question.”
11. Immanuel Kant
• Maintained that to understand the world
• around us, we must take account of our own
conceptual system.
– Our categories and concepts force us to see the
world in a certain way
– Some of what we see may be due to the
categories, concepts, and perspectives we bring
to our observation of the world, rather than being
part of the world as it really is in itself.
12. Noumena and Phenomena
• Kant distinguishes the noumena from the
phenomena:
– Noumena denotes reality as it exists in
itself, in its essence, independent of our
observation of it
– Phenomena are what we actually observe, our
own perceptions of the world as colored and
shaped by our perceptual and conceptual
apparatus
13. Analytic and Synthetic Statements
• An analytic statement is true by
definition, a statement in which the
predicate is contained in the subject.
• In a synthetic statement, the predicate is
NOT contained in the subject.
14. A Priori Knowledge
• A priori knowledge is knowledge that we
can gain purely through reason, without
• the need of observation.
• Analytic truths are known a priori because
they can be known to be true simply by
analyzing the concept.
15. A Posteriori Knowledge
• A posteriori knowledge follows or depends
on experience observation; it is an
empirical knowledge.
• Synthetic statements are known as a
posteriori.
16. Kant and A Priori Truths
• Are there any synthetic statements that can
be known a priori?
– Can we have a priori knowledge of facts about
the world purely through the use of reason?
• Kant argues that there is only one way such
truths could be possible:
– There are truths that we know with certainty
because they are built in to our conceptual and
observational capacities.
