Full Idea
Simonides claims that morality is doing good to one's friends and harm to one's enemies.
Gist of Idea
Simonides said morality is helping one's friends and harming one's enemies
Source
Plato (The Republic [c.371 BCE], 332d)
Book Reference
Plato: 'Republic', ed/tr. Waterfield,Robin [OUP 1993], p.10