Reason and experience
Michael Lacewing
© Michael Lacewing
• How do we know what we know?
• Types of knowledge
– Acquaintance: I know Oxford well.
– Know how: I know how to ride a bike.
– Propositional: I know that elephants are
• Belief v. knowledge
– Knowledge has a justification or evidence
A clear distinction
• Rationalism: we can have substantive a
priori knowledge of how things stand
outside the mind.
• Empiricism: we cannot.
Substantive knowledge
• Substantive knowledge is knowledge of a
synthetic proposition. Trivial knowledge is
knowledge of an analytic proposition.
– An analytic proposition is true or false in virtue
of the meanings of the words.
– Not all analytic propositions are obvious: ‘In five
days time, it will have been a week since the day
which was tomorrow three days ago’ - true or
A priori knowledge
• A priori: knowledge that does not
require (sense) experience to be
known to be true (v. a posteriori)
• It is not a claim that no experience was
necessary to arrive at the claim, but
that none is needed to prove it.
• How can there be a priori knowledge?
• Innate ideas: we have ideas or
knowledge ‘innately’
– We have an innate conceptual scheme
• A priori reasoning and intuition: we
have a form of rational ‘insight’
Innate ideas
• Locke’s attack
– All ideas (concepts and
propositional knowledge)
are available to
– There is no idea or claim
that everyone has from
– Children must first learn
or be taught concepts
• All concepts must be
gained from experience
Innate ideas
• No major philosopher has defended innate
ideas in Locke’s sense
• Innate ideas are ideas whose content cannot
be gained through experience.
• We do not have the idea/concept from birth
- experience must trigger our awareness of
the idea, but the idea is not derived from
• Triggering capacities: bird song, language
Innate ideas
• Core argument: experience is
insufficient for forming the concept
• E.g. ‘physical object’: how can
experience lead us to form the concept
of something that exists independently
of experience?
Origins of innate ideas
• Carruthers: innate ideas are genetically
encoded, so that under certain conditions, we
will develop the idea
• Descartes: innate ideas are part of our rational
nature, dispositions to form certain thoughts
through reasoning
• Plato: innate ideas are ‘remembered’ from a
previous existence
A priori reasoning about
what exists
• Can sense experience tell us about
everything that exists? Moral values? God?
• Can sense experience, on its own, give us
knowledge? What justifies the beliefs we
form on the basis of sense experience?
• Descartes: How do I know that reality is the
way I experience it?
– The problem of the evil demon
The physical world
• What causes our experiences of the physical world?
Physical objects
Evil demon
• Not me: I would know if I imagined them
• Not evil demon or God
– These options would entail that God is a deceiver
– God exists and is not a deceiver (ontological argument)
• Therefore, physical objects exist.
On human reasoning
• Can a priori reasoning establish
anything except analytic truths?
– Hume: ‘Nothing is demonstrable, unless
the contrary is a contradiction.’
• What can we know about the world
that does not depend on sense
Conceptual schemes
• Is sense experience where it all starts? Or
does something have to exist before sense
experience to make it ‘intelligible’?
– Is it a jumble before we apply concepts?
• Origins of concepts: language (other people)
v. structure of the mind (‘reason’)
– Language: different languages have different
concepts, so lead to different ways of
understanding sense experience
– Structure of the mind: this is common to
everyone, so there is only one (basic) way of
making sense of experience

Rationalism and empiricism