I wanted to respond to Mike's observation from Act II, scene 2 about how in marriage two people become one and with twins "one" person becomes two. Adriana says:
"For know, my love, as easy mayst thou fall
A drop of water in the breaking gulf,
And take unmingled thence that drop again,
Without addition or diminishing,
As take from me thyself and not me too." (2.2.136-140)
This echoes Antipholus of Syracuse's earlier concern about being discontented or without pleasure. He says:
"I to the world am like a drop of water
That in the ocean seeks another drop,
Who, falling there to find his fellow forth,
Unseen, inquisitive, confounds himself.
So I, to find a mother and a brother,
In quest of them, unhappy, lose myself." (1.2.35-40)
The unity between the images here is ironic. It unites Adriana with the wrong Antipholus, as if the figurative language of the play were suffering the same mistake of identity that the characters do. I find the image a beautiful one, capturing at once the individuality of the drop with the completeness of the belonging to the larger ocean. One of the themes raised is that Antipholus of Syracuse is looking to belong once again to a larger whole (family); Adriana is looking to belong again to a larger whole (husband/marriage). And with all the images of division at the beginning of the play -- twins separated at birth, Egeon about to be separated from his life, Antipholus of E. separated (spiritually) from his wife -- the ocean image reminds us of the completeness and wholeness of unification, even before the final line and image of the play: "Let us go hand in hand, not one before the other."