Iura inventa metu iniusti fateare necesse est
You must admit that law and justice are mere inventions and that their origin is the fear of injustice
Epicurus runs with ethical scepticism, adding, injustice is not an evil in itself but only in respect to its consequences. For Epicurus justice is a form of social contract created out of the above conditions.
For Aristotle justice and injustice had a particular nature that could be determined by common sense, contract was not necessary as it was within the nature of all men to determine such things by common sense.
P. Shorey, Horace Satires i. 3. 112-13 and Plato Theaetetus 172 A,B, Classical Philology, Vol 16, No.2 (April) 1921