Socrates asks Euthyphro whether something is pious because it is loved by the gods, or on the contrary whether something is loved by the gods because it is pious. We may replace “pious” with whatever we’d like – the term appears at least a little foreign to modern ears – and the question may be asked of justice, morality, of anything else of value under the sun. Is something valuable because the gods deem it so, or do the gods deem something valuable because there is some further reason which justifies their deeming? If the former, then value becomes brute and inexplicable: Socrates has forced Euthyphro to admit that the gods are irrational in their valuation, for there is no further reason explaining why it is they deem a thing to be of value. It simply is so. If the latter, then value is intelligible, and the gods perhaps rational – but, consequently, unnecessary to ground or determine value. For what is valuable is valuable on the basis of independent reasons: the gods do not determine what is valuable, but may rationally love what is valuable on the basis of its value. To put the dilemma in a sentence: in asking for the justificatory grounds of a religious prohibition or valuation, either the justification is an appeal to the unjustified will of the gods, or there is some independent basis for the justification – in which case appealing to the gods is extraneous. Either horn of the dilemma leads us to the conclusion that neither piety, nor morality, nor value, nor what-have-you, can be justified via appeal to divine will.

A similar dilemma emerges when we consider some formulations of moral relativism. Suppose one believes what Fred Feldman calls conceptual relativism: ‘that sentences of the form “act a is morally right” are either meaningless or else short for sentences of the form “act a is morally right in society S.”‘ Conceptual relativism relativizes the criterion for moral rightness to a society: what is right in one society may not be right in another. We tease out the Euthyphro dilemma by asking: on what basis would a society S justify that a particular act a is morally right or wrong in that society? Is action a morally right because society S deems it to be morally right; or does society S deem action a morally right because it is morally right? If the former, we end up at the unpalatable conclusion that there is no basis for society S deeming that any given act is morally right or wrong – it is a brute determination for which reasons cannot be provided. If the latter, then it turns out the moral rightness of an act is not relative to the judgments of a society but rather depends on the independent moral value of the act in question (which can in principle be justified). Conceptual relativism, though it seems to offer a criterion for determining whether an act is morally right or wrong, in fact can do nothing of the sort.

What similarity allows us, in both cases, to apply the dilemma? The dialogic nature of Euthyphro is instructive. To be in dialogue means to enter a space of mutual reasons. What is asserted must in principle be defensible – in other words, one can’t expect their interlocutor(s) to accept their claims at face value (though conversation most often proceeds smoothly through shared premise). One asserting X, in other words, cannot respond to the other who asks “why X?” by appealing to one’s bare assertion of X. Or, to put it another way, insofar as one fails to respond to a demand of producing the reasons underlying their assertions, one exits dialogue. One rather finds themselves in a wholly different space. Ostension, perhaps – a pointing at the bare brute fact of the matter (“…of course the ship is sinking,” to the incredulous crewmate, “would you just take a look at that hole?!”). Or rhetoric, insofar as one enacts a compliance of thought via deceit (and the relationship between rhetoric and dialogue, as Plato knew, is quite complex, quite deadly). To phrase it bluntly: the space of dialogue is the space of reason, and this cannot be doubted.

With this understanding we can frame Socrates’ question another way: do the gods occupy a space of reasons? Can we engage them in dialogue, even if only indirectly? How will they respond, asked on what basis they love what is just, what is moral? (Zeus: with a lightning bolt). And the dilemma, then, is this: either the gods dialogue, or they do not.

If they do, there is reason for what they do which undergirds what they value – reason in principle accessible to humanity. The gods in this case can disobey the moral law, as time and time again in the Greek mythos they do, for it is distinct from their whims and wishes. And so the gods can be no source for value, morality, or what have you. They drop out of the picture; their desires bear no more weight than yours or mine in our evaluation of the truth.

If the gods do not dialogue, however, then they definitionally and brutely act in accord with the moral law. In this case there is no further reason justifying whether their action is consistent with the moral law – what is moral, is moral simply because it is loved by the gods. To ask the gods, then, why it is they love what is moral, is to ask a question impossible to rationally answer. The implication, of course, is that morality is fundamentally irrational. All that is good and right fades to inscrutability and obscure; all that is holy is profaned.

What a mission, then, Plato (via Socrates) lays out for philosophy: to establish a dialogue with the gods.