Full Idea
Soul must be cause of good and evil, beauty and ugliness, justice and injustice, and all the opposites.
Clarification
'Soul' is the Greek word 'psuché', which covers mind and consciousness and life
Gist of Idea
Soul must be the cause of all the opposites, such as good and evil or beauty and ugliness
Source
Plato (The Laws [c.349 BCE], 896d)
Book Reference
Plato: 'The Laws', ed/tr. Saunders,Trevor J [Penguin 1970], p.427