Aegeon states that his two sons were so identical when they were young that they could be distinguished by name only, a claim that is deeply ironic, since much of the play's plot stems from the confusion brought about by the fact that his twin sons even share the same name—something he apparently does not know. He says:
There had she not been long but she became
A joyful mother of two goodly sons,
And, which was strange, the one so like the other
As could not be distinguished but by names
In narrating the events of his sons’ birth, Aegeon emphasizes that they resembled each other so closely that no physical feature could be used to tell them apart, adding that they're identical in all but name. As a result of the storm that divided his family, Aegeon has not seen his wife, nor one of his sons, since shortly after the birth. Ironically, then, he does not yet know that he and his wife have chosen the exact same name for their separated sons (Antipholus)—an absurd coincidence that he could hardly have anticipated.
In fact, Aegeon won’t discover that his sons share a name until the very end of the play, by which point this implausible coincidence has brought chaos to the lives of both Antipholus of Syracuse and Antipholus of Ephesus. This remarkable set of coincidences—that two identical twins share a name, as do their respective slaves, who are also identical twins—is essential to the comic plot of the play. Aegeon’s unknowing description of his sons as indistinguishable “but by names” becomes funnier and even more ironic as the various cases of mistaken identity unfold on the stage. What's more, once the audience discovers that the twins have the same name, the entire situation becomes an instance of dramatic irony, too, since the audience knows something crucial that Aegeon himself doesn't know.
Dramatic irony is perhaps the primary comedic tool employed by Shakespeare in The Comedy of Errors. There is, throughout the entirety of the play, a significant gap between characters’ understanding of their situation and the audience's understanding of the situation. This gap is emphasized at various points in the text, as characters respond with exasperation or fury to the various misunderstandings and mix-ups that drive the plot. Take, for example, this conversation between Antipholus of Syracuse and Dromio of Syracuse in Act 2, Scene 2:
ANTIPHOLUS OF SYRACUSE
How now, sir? Is your merry humor altered?
As you love strokes, so jest with me again.
You know no Centaur? You received no gold?
Your mistress sent to have me home to dinner?
My house was at the Phoenix? Wast thou mad,
That thus so madly thou didst answer me?DROMIO OF SYRACUSE
What answer, sir? When spake I such a word?
Antipholus of Syracuse is furious about what he perceives to be a prank by his slave, Dromio, who is likewise perplexed at his master’s fury. Unlike the characters, the audience knows that these scenes of disorientation stem from the two sets of twins’ unknown proximity to each other. In this case, it was Dromio of Ephesus who, misidentifying Antipholus of Syracuse for his own master, reported to him that he had never received any gold and recommended that he return home for dinner with his wife. Now, though, Antipholus of Syracuse grills Dromio of Syracuse about why he said such things—but Dromio didn't say these things. The stress and confusion that stems from the characters’ ignorance of this situation is the grounds for much of the play's comedy.
In one of the play’s few soliloquies, Antipholus of Syracuse wonders to himself about the strange and inexplicable friendliness he has encountered in Ephesus:
There’s not a man I meet but doth salute me
As if I were their well-acquainted friend,
And everyone doth call me by my name.
Some tender money to me; some invite me; […]
Sure these are but imaginary wiles,
And Lapland sorcerers inhabit here
In this soliloquy, the audience is given a window into Antipholus’s thoughts and feelings at this point in the play. He cannot believe the warmth and kindness with which he has been received by the Ephesians, who salute him as they would an old friend, invite him into their homes, and even somehow refer to him by his own name without ever having been introduced. Dramatic irony pervades the soliloquy, as the audience understands that the Ephesians greet him with such friendliness because they have misidentified him as his twin brother.
The suspicious Antipholus does not trust this warm welcome, speculating that the friendliness of the Ephesians is a strategy for trapping victims on the island. As of this soliloquy, Antipholus of Syracuse still believes that he is in a city populated by supernatural beings like sorcerers and ghosts who trick humans to wicked ends.
In a speech punctuated with dramatic irony, Dromio of Syracuse entreats Antipholus of Syracuse to stay another night in Ephesus on account of the supposedly kind and gentle nature of the Ephesians. He says:
Faith, stay here this night. They
will surely do us no harm. You saw they speak us
fair, give us gold. Methinks they are such a gentle
nation that, but for the mountain of mad flesh that
claims marriage of me, I could find in my heart to
stay here still, and turn witch
The audience knows what Dromio does not: that the seemingly “giving” nature of the Ephesians stems from a case of mistaken identity. The Ephesians are not, as Dromio of Syracuse here supposes, some sort of supernatural race that grants blessings to travelers, and every “gift” the Syracuse twins receive comes, unbeknownst to them, at the expense of their Ephesus counterparts.
Dromio is so moved by what he misidentifies as generosity that he even claims he could “turn witch,” joining the magical residents of Ephesus in their supernatural pursuits, except for the fact that he is not attracted to the woman who believes herself to be his wife, Luce, whom he describes unflatteringly as a “mountain of mad flesh."
