PLATO
(427-347 BCE)

Theory of the Forms

Metaphysical Problem
Problem of identity (being) and change (becoming)
- Heraclitus - "You can never step in the same river twice"
- Parmenides - "All is one"

Meta-Ethical Problems
The meaning of "good"
- subjective: Sophists
- objective: Plato
Problem of normative knowledge
- ethical skepticism: Sophists
- ethical knowledge: Plato 

A states "X is Y"

Subjective
Statement about the belief, opinion, or perspective of A (the subject); viz., Y is the opinion, belief, or perspective of A about X
Neither True nor False
    It may be true or false that A believes that "X is Y" but whether or not X has the property Y is not itself at issue
Knowledge of truth or falsity of statement is theoretically impossible since opinion itself is neither true or false
Objective
Statement about X (the object); viz., that X has the property Y
True or False
    True if X has the property Y
    False if X does not have the property Y
Knowledge of truth or falsity of statement is theoretically possible since this is purportedly a statement of fact

The Realms 

Being

    The Realm of the Forms    

Universal

Perfect

Eternal

Non-spatial

Essence

Identity

Reason

Knowledge

Becoming

    The Realm of the Physical    

Particular

Imperfect

Temporal

Spatial

Appearance

Change

Sense

Belief

INDEPENDENT

DEPENDENT
 Participates

Theory of the Forms

Metaphysical Problem
Coexistence of identity (being) and change (becoming) in distinct realms

Meta-Ethical Problems
The meaning of "good"

objective: dependent on participation, not the individual person

Problem of normative knowledge

ethical knowledge: whether or not participates is a theoretically knowable matter of fact, not opinion

Republic, Book VII
"The Allegory of the Cave"