Plato’s Theory of
Knowledge and the
Doctrine of the Forms
Socrates’ Heritage
 Ethical conduct must be founded on knowledge.
 Real knowledge must be knowledge of eternal
values which are not subject to the impressions of
the senses or subjective opinions but are the same
for all people and all ages.
 Plato’s conviction: there can be knowledge in the
sense of objective and universally valid
knowledge.
Main Arguments
 Knowledge is not Sense-Perception: the mind’s
activity is necessary.
 Knowledge is not “True Judgment”: a
judgment may be true without the fact of its truth
involving knowledge on the part of the person
who makes the judgment.
 Real knowledge: concern the universal, abiding,
stable, unchangeable. To each true universal
concept there corresponds an objective reality.
Hierarchy of Knowledge
The State of Mind Corresponding Objects
noesis
originals (arkhai)
Episteme
(Knowledge) dianoia
mathematics
Doxa
(Opinion)
pistis
eikhasia
zoa (real objects)
eikhones (images)
Theory of the Forms
 Forms or Ideas: universal, real, objective,
unchanging essences.
 These Forms are the objects of true knowledge.
 Sensible things are copies or participations in
these universal realities.
 One Form is central to the being and knowability
of all the others: the Form of the Good (Republic
505a-509c).
 Hence the Theory of the Two Worlds: the Ideal
World and the Sensible World.
Significance
 Breaking away from the materialism of the preSocratics, asserting the existence of immaterial
and invisible Being, a stable and abiding Reality.
 Agreeing with Heraclitus that sensible things are
in a state of flux or becoming. They are not fully
real, but they are not mere Non-being, as they
have a share in being.
 Going beyond the interests of the Sophists and
Socrates in ethical standards and definitions into
the sphere of ontology.