Why does Sophocles open Antigone with a dialogue between sisters?

Antigone opens with a dialogue between Antigone and Ismene, the daughters of Oedipus. In their dialogue, the two sisters discuss the death of their brothers, Eteocles and Polynices, as well as the decree of Creon, their uncle, that makes burying Polynices a crime punishable by death, since Polynices had led hostilities against Thebes. The dialogue serves not only as exposition, but also to highlight the difference between the two sisters, and thus the remarkability of...

Antigone opens with a dialogue between Antigone and Ismene, the daughters of Oedipus. In their dialogue, the two sisters discuss the death of their brothers, Eteocles and Polynices, as well as the decree of Creon, their uncle, that makes burying Polynices a crime punishable by death, since Polynices had led hostilities against Thebes. The dialogue serves not only as exposition, but also to highlight the difference between the two sisters, and thus the remarkability of Antigone's stated intentions to defy the law and bury their brother.

The opening dialogue between Antigone and Ismene serves as exposition for the play. Through the dialogue, we learn the basis for the important familial relationships, as well as the political ones, in the play. From the sisters’ discussion, we know what law Creon has declared and why he has declared it. We are also able to see the reactions from his nieces to help us understand the emotional state of not just the characters, but Thebes as well.

In addition to exposition, the dialogue gives us insight into the major conflict of the play—Antigone's desire to bury Polynices even in the face of Creon's proclamation and the announced punishment. Through the discussion between the sisters, we come to see the depth of Antigone’s conviction. We also see the contrast between the sisters.

Antigone is moved to do what she believes to be right, whereas Ismene admits that she does not have the strength to break the law. Interestingly, they both seem to be trying to overcome the stigma on their family, but they are doing so in different ways. Ismene is trying to break away from the actions of the past by following the law rather than flouting it, whereas Antigone is following in her father's and brothers' footsteps in putting her own ideas of what needs to be done over the good of the state.

Antigone’s conviction is remarkable as it stands in the face of not only the law, but the perception of the law as being for the public good, a sentiment voiced by Ismene during their conversation. We see through this that what Antigone is planning goes not just against the law, but against the perceptions of the other citizens as well. Thus, the dialogue between the sisters serves to show Antigone’s uniqueness as well as providing exposition and setting the context for the rest of the play.