Socrates now changes the direction of the inquiry, asking Euthyphro whether holy deeds are approved by the gods because they are holy or whether they are holy because they are approved by the gods. To illustrate his point, Socrates draws the distinction between being x and getting x. Something carried is being carried because it gets carried: it does not get carried because it is being carried. "Being carried" is the state of the object that is being carried, the state of the object that is acted upon. "Getting carried" is the action of which that the object is on the receiving end. In saying that something is being carried because it gets carried, Socrates is arguing that an object can only be in the state of being carried if someone decides to carry it--that is, if it gets carried. A thing becomes changed because something else changes it: it does not get changed by something else because it is already a changed thing.
Socrates then draws a similar distinction between being approved and getting approved. A thing is being approved because it gets approved, and not the other way around. We cannot say that it gets approved--that someone decides to approve of it--because it is already being approved by that someone. According to Euthyphro's definition, something gets approved by the gods because it is holy and not the other way around: it is not holy because it gets approved by the gods. And because it gets approved it is being approved, and thus is something that is approved by the gods.
It follows from this argument however, that what is holy is something different from what is approved of by the gods. Something holy gets approved because it is holy, and something that is being approved by the gods is being approved of because it gets approved. If what is being approved of by the gods were the same thing as what is holy, and if what is holy gets approved because it is holy, then what is being approved of by the gods would get approved because it is being approved of, when in fact the opposite is true. Alternatively, if we accept that what is being approved of is being approved of because it gets approved, then the holy, too, would have to be holy because it gets approved, and not the other way around.
Though the argument Socrates' presents here sounds quite complicated and is very difficult to state clearly, it is actually relatively simple. Under discussion are three things we might say about a certain deed, and three claims Euthyphro is committed to. The three things we might say about a certain deed are:
(A) It is holy
(B) It gets approved of by the gods
(C) It is divinely approved
The distinction between (B) and (C) is that (B) deals with the act of approval on the part of the gods and (C) deals with the state of the deed as being approved of by the gods. Socrates' earlier point, about something being approved because it gets approved and not vice versa, is meant to point out that we would have (C) only because of (B), and not the other way around. That is, a deed is in the state of being approved of by the gods because the gods decided to approve of it. The reverse, that the gods decide to approve of a deed because it is a deed they approve of, is nonsensical.
The three claims Euthyphro is committed to are:
(i) Something gets approved by the gods because it is holy
(ii) Something is approved of by the gods because it gets approved of by the gods
(iii) What is holy is what is approved of by the gods
In other words, (i) states that if (A) then (B), (ii) states that if (B) then (C), and (iii) states that (A) = (C). The problem is that (i) and (ii) imply that if (A) then (C), not (A) = (C). If (A) determines (B) and (B) determines (C), then Euthyphro cannot claim that (A) and (C) are one and the same.
We should note that it is possible that (A) and (C) refer to the same deeds. If everything that is divinely approved gets approved by the gods (which seems almost irrefutable) and if everything that gets approved by the gods is holy, then what is holy and what is divinely approved of are the same things. The point Plato is making is not that (A) and (C) necessarily refer to different things, but that even if they do refer to the same things, they do not have the same meaning. For instance, every creature that has a heart also has a kidney, but "creature with a heart" and "creature with a kidney" do not mean the same thing, and cannot be said to be equivalent even if they refer to exactly the same things. Similarly, Plato wants to suggest, what is holy and what is approved of by the gods do not mean the same thing and cannot be said by Euthyphro to be equivalent.
This argument is a very forceful move against the idea of morality as being determined solely by some kind of divine authority. For example, in the Judeo- Christian tradition, we might be tempted to say that what is good is good because God says it's good, but we have not made ourselves sufficiently clear. Does God approve of it because it is good, or is it good because God approves of it? And, following Plato's argument, does this mean that what is good and what God approves of are two different things that cannot be equated? Because of arguments like this one, modern ethical theory tries to ground moral responsibility in our own autonomy rather than in God, regardless of whether the philosopher in question believes in God.
Socrates is treating Euthyphro as the teacher when in fact Socrates is teaching Euthyphro
Plato suggesting that there is no such thing as a definition of holiness, that there is no one feature that all holy deeds have in common?
What Plato/Socrates is challenging is Euthyphro's/everyone's knowledge or assumed knowledge of anything, not the can we know anything idea, but have we challenged our beliefs? Are we sure that the conclusion we hold is conclusion enough? Peirce and James pick this up again a few years later.