Socrates encounters Euthyphro outside the court of Athens. Socrates has been called to court on charges of impiety by Meletus, and Euthyphro has come to prosecute his own father for having unintentionally killed a murderous hired hand. Socrates flatters Euthyphro, suggesting that Euthyphro must be a great expert in religious matters if he is willing to prosecute his own father on so questionable a charge. Euthyphro concurs that he does indeed know all there is to be known about what is holy. Socrates urges Euthyphro to instruct him and to teach him what holiness is, since Euthyphro's teaching might help Socrates in his trial against Meletus.
First, Euthyphro suggests that holiness is persecuting religious offenders. Socrates finds this definition unsatisfying, since there are many holy deeds aside from that of persecuting offenders. He asks Euthyphro instead to give him a general definition that identifies that one feature that all holy deeds share in common. Euthyphro suggests that what is holy is what is agreeable to the gods, in response to which Socrates points out that the gods often quarrel, so what is agreeable to one might not be agreeable to all.
Euthyphro's most important attempt to define holiness comes with his suggestion that what is holy is what is approved of by all the gods. Socrates sets up a rather elaborate argument to show that the two cannot be equivalent. What is holy gets approved of by the gods because it is holy, so what is holy determines what gets approved of by the gods. And what gets approved of by the gods in turn determines what is approved of by the gods. It follows from this reasoning that what is holy cannot be the same thing as what is approved of by the gods, since one of these two determines what gets approved of by the gods and the other is determined by what gets approved of by the gods.
Euthyphro is next led to suggest that holiness is a kind of justice, specifically, that kind wh...