“Natural justice is a pledge of mutual benefit to refrain from harming one another and not to be harmed.”Epicur · Maximele fundamentale · -280 · Maxima 31
Justice is a mutual contract: give up harming so you won't be harmed.
Epicurus gives justice a contractual definition: it is not a cosmic order but an arrangement advantageous to both sides. The mechanism is rational: each person gives up the option of harming in exchange for protection from being harmed, a trade no rational being would refuse. It follows that an unjust law, one that fails to serve this exchange, loses its authority. Traffic rules work exactly this way, as a mutual pact, not a divine command.
Why it matters Supports critical thinking about laws and norms: ask whether a rule protects everyone mutually or serves only a few.