A short Socratic dialogue by Plato. One of my personal favorites. Socrates encounters a priest, Euthyphro, and asks him to define the concept "piety" that he might understand the charges brought against him by Meletus that he faces in the trial written about in The Apology (Apologia).

Socrates employs the elenchus (refutation), sometimes known as The Socratic Method, to show Euthyphro the contradictions in the set of beliefs that he holds in his area of expertise.

"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, for you agreed that all impious actions are impious and all pious actions pious through one form ... tell me then what this form itself is, so that I may look upon it, and using it as a model, say that any action of yours or another's that is of that kind is pious, and if it that it is not."

At this inquiry, Euthyphro proceeds to recite several versions of The Divine Command Theory, and Socrates promptly fillets him.