How does Abigail Williams add to the dramatic effect of "The Crucible"?
Abigail is the ultimate drama queen. She IS most of the drama in "The Crucible." From the moment that we meet her in act one, to the end when she bails on Salem, she adds dramatic impact. One of the first additions of drama is when she threatens the girls, "I will bring a pointy reckoning that will shudder you" if they mention that she was attempting to kill off Goody Proctor. First of all, we realize Abby is a jealous girl, willing to kill someone; secondly, that she uses threats and intimidation to keep that secret. Then, enter John Proctor, who she sidles up to and rather dramatically attempts to flirt with. Her affair with John adds dramatic impact--the plot thickens, we understand her attempted murder, and wonder what is going to happen. To top it off in act one, Abby is the one who starts the hysterical witch hunt when she bursts forth with "I want to open myself!...I saw Sarah Good with the devil!" And this was after she turned them all onto Tituba as a potential witch, to save her own skin.
From that point on, Abby led most of the accusations of witchcraft. She was the ringleader. She even sticks herself in the belly with a needle in order to get Elizabeth, an upstanding and righteous woman, arrested. That prompts Proctor and other townsfolk to action, to try to save their wives. Her dramatic antics in that regard are the reason that we have act three. And then, in the court, she plays the whole "Mary Warren is an evil witch-bird" act, which turns Mary against John, and all of John's attempts to free the innocent are thwarted.
For all of these reasons and more, Abby is the central figure of dramatic tension, action and impact in "The Crucbile." I hope that those thoughts help a bit; good luck!
Miller's use of Abigail Williams adds to the dramatic effect of the play by creating a classic, yet relevant, twist--the love triangle. By adding John and Abby's past relationship, Miller produces an entirely new layer of intrigue to a town and situation already rife with jealously, resentment, and political/religious conflicts. As Abigail becomes the dramatic center of the conflict, all other actions revolve not only around her decisions and actions, but also the decisions and actions of others caused by her relationships with and secrets about them. Without Abby, Betty would not have been frightened by her actions in the woods and caused John Hale to be summoned, John would have had no secret to keep from the town, and Elizabeth would have had no reason to lie to protect John when she speaks to Judge Danforth in Act III. Abby is what Miller uses to take a tragic story of religious passion-gone-wrong into the timeless study of human behavior it has become today.