Full Idea
The justice of nature is a pledge of reciprocal usefulness, neither to harm one another nor to be harmed.
Gist of Idea
Justice is a pledge of mutual protection
Source
Epicurus (Principle Doctrines ('Kuriai Doxai') (frags) [c.290 BCE], 31)
Book Reference
Epicurus: 'The Epicurus Reader', ed/tr. Inwood,B. /Gerson,L. [Hackett 1994], p.35
A Reaction
Notice that justice is not just reciprocal usefulness, but a 'pledge' to that effect. This implies a metaethical value of trust and honesty in keeping the pledge. Is it better to live by the pledge, or to be always spontaneously useful?