Plato never speaks in his own voice in his dialogues, and speaks as Socrates in all but "the Laws". In the "Second Letter", it says, "no writing of Plato exists or ever will exist, but those now said to be his are those of a Socrates become beautiful and new"; if the Letter is Plato's, the final qualification seems to call into question the dialogues' historical fidelity. In any case, Xenophon's "Memorabilia" and Aristophanes's "The Clouds" seem to present a somewhat different portrait of Socrates from the one Plato paints. The Socratic problem asks how to reconcile these various accounts. Leo Strauss notes that Socrates' reputation for irony casts doubt on whether Plato's Socrates is expressing sincere beliefs.