All these circumstances stated by Diodorus are not only completely different from Xenophon, but irreconcilable with his conception of the event. We must reject either the one or the other.
Now Xenophon is not merely the better witness of the two, but is in this case sustained by all the collateral probabilities of the case.
1. Diodorus represents the Athenians as having despatched by public vote, assistance to Thebes, in order to requite the assistance which the Thebans had before sent to restore the Athenian democracy against the Thirty. Now this is incorrect in point of fact. The Thebans had never sent any assistance, positive or ostensible, to Thrasybulus and the Athenian democrats against the Thirty. They had assisted Thrasybulus underhand, and without any public government-act; and they had refused to serve along with the Spartans against him. But they never sent any force to help him against the Thirty. Consequently, the Athenians could not now have sent any public force to Thebes, in requital for a similar favor done before by the Thebans to them.
2. Had the Athenians passed a formal vote, sent a large public army, and taken vigorous part in several bloody assaults on the Lacedæmonian garrison in the Kadmeia,—this would have been the most flagrant and unequivocal commencement of hostilities against Sparta. No Spartan envoys could, after that, have gone to Athens, and stayed safely in the house of the Proxenus,—as we know from Xenophon that they did. Besides,—the story of Sphodrias (presently to be recounted) proves distinctly that Athens was at peace with Sparta, and had committed no act of hostility against her, for three or four months at least after the revolution at Thebes. It therefore refutes the narrative of Diodorus about the public vote of the Athenians, and the public Athenian force under Demophon, aiding in the attack of the Kadmeia. Strange to say,—Diodorus himself, three chapters afterwards (xv, 29), relates this story about Sphodrias, just in the same manner (with little difference) as Xenophon; ushering in the story with a declaration, that the Athenians were still at peace with Sparta, and forgetting that he had himself recounted a distinct rupture of that peace on the part of the Athenians.
3. The news of the revolution at Thebes must necessarily have taken the Athenian public completely by surprise (though some few Athenians were privy to the scheme), because it was a scheme which had no chance of succeeding except by profound secrecy. Now, that the Athenian public, hearing the news for the first time,—having no positive act to complain of on the part of Sparta, and much reason to fear her power,—having had no previous circumstances to work them up, or prepare them for any dangerous resolve,—should identify themselves at once with Thebes, and provoke war with Sparta in the impetuous manner stated by Diodorus,—this is, in my judgment, eminently improbable, requiring good evidence to induce us to believe it.
4. Assume the statement of Diodorus to be true,—what reasonable explanation can be given of the erroneous version which we read in Xenophon? The facts as he recounts them conflict most pointedly with his philo-Laconian partialities; first, the overthrow of the Lacedæmonian power at Thebes, by a handful of exiles; still more, the whole story of Sphodrias and his acquittal.
But assume the statement of Xenophon to be true,—and we can give a very plausible explanation how the erroneous version in Diodorus arose. A few months later, after the acquittal of Sphodrias at Sparta, the Athenians did enter heartily into the alliance of Thebes, and sent a large public force (indeed five thousand hoplites, the same number as those of Demophon, according to Diodorus, c. 32) to assist her in repelling Agesilaus with the Spartan army. It is by no means unnatural that their public vote and expedition undertaken about July 378 B.C.,—should have been erroneously thrown back to December 379 B.C. The Athenian orators were fond of boasting that Athens had saved the Thebans from Sparta; and this might be said with some truth, in reference to the aid which she really rendered afterwards. Isokrates (Or. Plataic. s. 31) makes this boast in general terms; but Deinarchus (cont. Demosthen. s. 40) is more distinct, and gives in a few words a version the same as that which we find in Diodorus; so also does Aristeides, in two very brief allusions (Panathen. p. 172, and Or. xxxviii, Socialis, p. 486-498). Possibly Aristeides as well as Diodorus may have copied from Ephorus; but however this may be, it is easy to understand the mistake out of which their version grew.
5. Lastly, Plutarch mentions nothing about the public vote of the Athenians, and the regular division of troops under Demophon which Diodorus asserts to have aided in the storming of the Kadmeia. See Plutarch (De Gen. Socrat. ad fin. Agesil. c. 23; Pelopid. 12, 13). He intimates only, as Xenophon does, that there were some Athenian volunteers who assisted the exiles.
M. Rehdantz (Vitæ Iphicratis, Chabriæ, etc. p. 38-43) discusses this discrepancy at considerable length, and cites the opinion of various German authors in respect to it, with none of whom I altogether concur.
In my judgment, the proper solution is, to reject altogether (as belonging to a later time) the statement of Diodorus, respecting the public vote at Athens, and the army said to have been sent to Thebes under Demophon; and to accept the more credible narrative of Xenophon; which ascribes to Athens a reasonable prudence, and great fear of Sparta,—qualities such as Athenian orators would not be disposed to boast of. According to that narrative, the question about sending Athenians to aid in storming the Kadmeia could hardly have been submitted for public discussion, since that citadel was surrendered at once by the intimidated garrison.