Socrates expects satisfactory definitions to do some sort of explanatory job. At the most elementary level, this job is that of what I shall call “explaining content.” I'll start by explaining the content of that phrase, and then, after yet another look at Euthyphro 6de, turn to one passage in which a definition is failed because it does not explain content: Euthyphro 9d–11b.

EXPLAINING CONTENT

Consider the following dialogue schema:

1. Q1: What's that?

2. A1: It's an F.

3. Q2: Why is it an F?

4. A2: Because it is H, and F=df the H.

At a minimum, Socrates expects someone with a proper definition for courage, piety, or whatever, to be able to use it in the way A does here.

Consider Q2. It is vague: it may have different forces in different contexts.

It might be that Q is not a native speaker of English, A knows this, and uses “G” to define “F” on this occasion because he knows that the words that compose “G” are English words known to Q. He might define “F” quite differently for another speaker. If Socrates were only requiring this much of definitions, it would just be a question of explaining the content of a term in a way that would make the use of the term comprehensible to a given audience.

Plainly Socrates wants more: he expects the correct definition to explain the content of the term on every occasion in which explanation is demanded.