While heading to court to answer charges of corrupting the youth, Socrates meets up with Euthyphro who is reporting his father for murder. Many believe Euthyphro crazy to prosecute his own father. Euthyphro seems so sure that his deeds are correct and pious. Socrates, hoping to learn the nature of piety that it might help him with his own legal woes, begins a philosophical dialogue with Euthyphro.
Euthyphro’s first definition of piety is that one should prosecute the wrongdoer no matter what their relation. My own objection would be that this is a bit of circular reasoning in that it defines the concept by the act he wants to justify as being pious in the first place. Turning your father in who committed murder is pious because piety is turning your father in if he does wrong. Socrates rejects this definition on the grounds that it is an example and not the essential definition of piety:
Bear in mind then that I did not bid you tell me one or two of the many pious actions but that form itself that makes all pious actions pious.
Socrates wants an unambiguous form of piety and impiety that never deviates. He wants an unmovable truth. He wants the Essence of piety, its form.
Euthyphro’s second definition of piety is that piety is that which is dear to the gods. Euthyphro tries to justify his first definition by turning to mythology and talking about how Zeus whom he calls the best and most just of the gods punished his own father, Kronos, for his indiscretions. Socrates asks him if he believes in all the myths about the wars between the gods, which he answers with an affirmative. Socrates plants this seed early, and then uses it to deflect this second definition. He points out that the gods not only fail to always agree with each other, but that their disagreements often revolve around seminal human issues such as what is just and unjust. One god might think an action just, while another might declare it unjust.* This means any particular action can be both pious and impious depending on the perspective of the particular god in question, which creates a contradiction (as an action cannot be both pious and impious), therefore this definition must be rejected.
Euthyphro’s third attempt defines piety as what all the gods love and impiety as what all the gods hate. Socrates responds to this with an elaborate word-game noting the difference between the being who performs an action with the thing that is being acted upon. He does this, however, to note how the action is caught up with what the actor is doing: an object is seen because it is in the process of being seen. He draws on this argument to separate what is god-loved from what is pious. The gods might love piety, but that does not mean everything the gods love is pious. This is the most complex part of the dialogue. To simplify, the real problem with Euthyphro’s definition here is that it tells us nothing about the nature of piety, but only about a quality of piety: it is something the gods love. It confuses a characteristic of piety with its definition.
At this point Euthyphro gets frustrated. Socrates decides to help him out, hinting that piety is a part of justice, a sub-category; piety is justice in relation to the gods. Euthyphro never quite picks up on this thread that Socrates offers, but instead he offers a fourth definition that gets closer, but still misses the mark.
The fourth definition of piety offered is that piety is the part of the just that is concerned with the care of the gods. They compare the relationship of the gods to man to the relationship between master and slave. Socrates asks him what the gods aim to achieve by using humans as servants. Euthyphro claims piety is meant to preserve social order. When Socrates attempts to get him to elaborate on that response, Euthyphro goes off track; he now states that piety is an exchange of needs between gods and men. Socrates wonders what the gods could possibly need from men. How is a burnt offering something the gods need? Euthyphro responds that it isn’t that they need it, but rather it is pleasing to them. Socrates notes that they have basically returned to an earlier definition that has since been rejected: what is pious is once again what is dear to the gods. At this point Euthyphro has had enough.
Besides the central philosophical issues, Plato displays many literary chops in his dialogues. He could have just written a straight-forward dialogue dealing with the nature of piety, but there is more to it than that. The context of this dialogue is that Socrates is on his way to being charged with impiety towards the gods and for corrupting the youth of Athens. By adding this context as part of the dialogue, Plato is setting up an ironic situation in order to reveal the ridiculousness of the charges. Socrates delays his arrival to address these accusations in order to discuss the nature of piety; he isn’t impious, but rather he wants to get it right. Secondly, he is challenging the justifications of Euthyphro, a youth of Athens, for turning against his father. This also shows that Socrates’ behavior is the complete opposite of the charges against him.
* In fact, much Greek Tragedy builds off this very conflict (one quick example would be Aeschylus’ Eumenides).