Socrates often mentions that he is guided by a daemon, a kind of divine spirit, oracle, or “sign,” that takes the form of an inner voice or non-vocal nudge. The guide never tells Socrates what to do. It only indicates when Socrates is not to do something.
This distinction is important. One way to tell that a dialogue is spurious is if it has Socrates’ daemon tell someone else what to do.
Socrates learned over time to listen to this inner divine voice. He acted in service to it. Nothing that he does in his life is untouched by this inner divine voice.
He describes it in the Apology:
You have heard me speak at sundry times and in diverse places of an oracle or sign which comes to me, and is the divinity which Meletus ridicules in the indictment. This sign, which is a kind of voice, first began to come to me when I was a child; it always forbids but never commands me to do anything which I am going to do. This is what deters me from being a politician.
Later, he explains that the defense he is giving to the Athenian court has been approved by this inner divine voice.
Hitherto the divine faculty of which the internal oracle is the source has constantly been in the habit of opposing me even about trifles, if I was going to make a slip or error in any matter; and now as you see there has come upon me that which may be thought, and is generally believed to be, the last and worst evil. But the oracle made no sign of opposition, either when I was leaving my house in the morning, or when I was on my way to the court, or while I was speaking, at anything which I was going to say; and yet I have often been stopped in the middle of a speech, but now in nothing I either said or did touching the matter in hand has the oracle opposed me. What do I take to be the explanation of this silence? I will tell you. It is an intimation that what has happened to me is a good, and that those of us who think that death is an evil are in error. For the customary sign would surely have opposed me had I been going to evil and not to good.
Commentators throughout the centuries wonder at what it was that drove Socrates to be the Athenian gadfly, the devoted citizen and warrior, the one who chose poverty over charging his students or any who would listen to his one-on-one conversations.
This divine inner voice spoke inwardly to him, moving him to be the true hero of the Athenian people, being a corrective to their hubris. Along the way, Socrates became a true hero of the Greek people and western civilization; and he became so effective that they killed him for it.
Almost 500 years later, Plutarch wrote a dialogue on this daemon of Socrates. It is included in this anthology.
from the Editor’s Introduction: The Best Complete Plato