Alcibiades: I approve of A.
Socrates: But then surely you have a reason for your approval?
Alc.: Certes. I approve of A because it lacks property X!
Soc.: But then you must also approve of B, because B also lacks property X.
Alc.: What? No! That is awful. A is worthy because of... because of condition Y.
Soc.: Is it Y now? But condition Y applies also to action C. So you must approve of...
Alc.: I do not! How dare you compare A to C!
Soc.: It was thou who made the comparison, bold Alcibiades, when you said that it was condition Y that made A worthy. Since C also follows from condition Y, then C must also be worthy. If it is not so, then there must be some other reason why A is acceptable to you and B and C are not.
Alc.: Surely. A is acceptable because of reason Z.
Soc.: You are fast running out of reasons. And do not call me 'Shirley.' But you do wit, do you not, that if Reason Z is true, the D must also follow.
Alc.: D is an abomination. You cannot be saying that A is the same as D! That is a vile insinuation.
Soc.: Too bad they stopped teaching analogies a generation ago. To say that if A is justified by D, then D is just as well justified is not to say that A and D are the same thing; only that the reasons you present to justify the one are also sufficient to justify the other. You cannot cite X to support A and then ignore it in the case of B. You must think things through -- break on through to the other side, as the Poet once said. Or else do not lean upon that particular reed.
Alc.: Very well, then. I deny all reasons, lest they be argued against my other commitments. I assert the acceptability of A, simply as a brute fact. I approve of it simply because I approve of it.
Soc.: But then you are being unreasonable - literally. You desire A because you desire it, and nothing must stand between A and your unrestrained appetites. Begone, thou Nietzschean lout!
Plato: Solve for A.