In Meditation on the Common Concept of Justice (ca. 1703), Leibniz made points that deserve to be quoted at length. Editor Patrick Riley notes that “Leibniz’ radical formulation of this question follows Plato’s Euthyphro (9E-10E) almost literally, though Plato was dealing with ‘holiness’ rather than justice” (Leibniz, Political Writings, p. 45).
Leibniz says, “It is agreed that whatever God wills is good and just. But there remains the question whether it is good and just because God wills it or whether God wills it because it is good and just: in other words, whether justice and goodness are arbitrary or whether they belong to the necessary and eternal truths about the nature of things, as do numbers and proportions” (ibid).
For present purposes, what is important is whether justice and goodness depend on an arbitrary will or have criteria of their own, not whether those criteria are necessary and eternal.
To say that justice and goodness depend upon an arbitrary will “would destroy the justice of God. For why praise him because he acts according to justice, if the notion of justice, in his case, adds nothing to that of action? And to say… my will takes the place of reason, is properly the motto of a tyrant” (pp. 45-46; brackets in original).
“This is why certain persons, too devoted to the absolute right of God, who have believed that he could justly condemn innocent people and even that this might actually happen, have done wrong to the attributes that make God lovable, and, having destroyed the love of God, they left only fear [behind]” (p. 46; brackets in original).
“Thus all [Lutheran] theologians and most of those of the Roman Church, and also most of the ancient Church Fathers and the wisest and most esteemed philosophers, have been for the second view, which holds that goodness and justice have their grounds… independent of will and of force.”
“Plato in his dialogues introduces and refutes a certain Thrasymachus, who, wishing to explain what justice is, [says] that is just… which is agreeable or pleasant to the most powerful. If that were true, there would never be a sentence of a sovereign court, nor of a supreme judge, which would be unjust, nor would an evil but powerful man ever be blameworthy. And what is more, the same action could be just or unjust, depending on the judges who decide, which is ridiculous. It is one thing to be just and another to pass for it, and to take the place of justice.”
“A celebrated English philosopher named Hobbes, who is noted for his paradoxes, had wished to uphold almost the same thing as Thrasymachus: for he wants God to have the right to do everything, because he is all-powerful. This is a failure to distinguish between right and fact. For what one can do is one thing, what one should do, another” (pp. 46-47; brackets added).
“[I]f power were the formal reason of justice, all powerful persons would be just, each in proportion to his power; which is contrary to experience.”
“It is thus a question of finding this formal reason, that is to say, the why of this attribute, or this concept which should teach us what justice is” (p. 48). By “formal” Leibniz here means something like “essential”.