Plato describes "The Form of the Good" in his book, The Republic, using Socrates as his mouth piece. The Form of the Good is the ideal or perfect nature of goodness, and so an absolute measure of justice. Plato also explains his theory of justice in The Republic, in relation to his conception of the ideal state, both of which necessitate rule of the rational mind; in other words, philosopher-kings, who can grasp the Form of the Good.

Plato said that the highest form of knowledge is the form of the good, from which things that are just gain their usefulness and value. Humans have a duty to pursue the good, but no one can hope to do this successfully without philosophical reasoning.

From goodness is something called the "Hierarchy of Forms". This suggests that from goodness comes such things as justice, truth, equality and beauty, among many others. There are abstract ideas, for example horse, chair and tree. Beneath this are the mathematics and sciences, which train us to understand the abstract ideas. At the very bottom are the material objects - the opinions based on perception.

See also

• Theory of forms

Platonism | Deities