The original question had to be clarified through editing. Ismene impacts the plot development of the drama primarily because she represents the fundamental stratification against which Antigone fights. Ismene believes in the most basic of senses that she, as a woman, is not representative of the resistance and dissent that Antigone displays. Ismene moves the plot in the drama through her presence of the traditional Greek woman. She embodies what Antigone struggles against and she also demonstrates how far Antigone must go in order to receive validation as a human being. At the same time, I think that Ismene operates in a muted sense of sadness. At the very least, Antigone is able to speak out her anger and resentment. Ismene cannot speak the immense pain she experiences at the loss of her siblings, as well as the repudiation she experiences from her own sister. It is here where Ismene operates in moving the plot. She embodies that for all of Antigone's voice and articulation, the fundamental pain of being a woman in Greek society cannot be fully averted. Ismene is left to wallow in pain that is not fully recognized by either Greek society on the grounds of being a woman and by the audience, so taken in with Antigone's plight and predicament.