The fountain pen and the ballpoint pen help the audience to understand the conflict between Sister Aloysius and Father Brendan and also the way that both characters operate. To Sister Aloysius, the fountain pen is her preferred writing implement because she feels having a ballpoint pen makes it "too easy" for children to write and to just simply put down anything they want. It is far better, she argues, to have to slow down and think deliberately about every word before writing it, shown through the rather laborious process of having to dip the fountain pen in ink before continuing. Father Brendan on the other hand uses a ballpoint pen, and this is symptomatic of his progressive and modern ways, she feels. The process of using a fountain pen therefore suggests the kind of character that Sister Aloysius is: deliberate, decided, and, once she has made up her mind, unstoppable. This is shown through her allegations that sexual abuse has taken place. Note what she says to Father Brendan about the certainty of her convictions:
I will step outside the church if that's what needs to be done, till the door should shut behind me! I will do what needs to be done, though I'm damned to Hell! You should understand that, or you will mistake me.
Just like every word that is written with a fountain pen must be carefully thought through and debated before it is set down, so too are the beliefs of Sister Aloysius considered very carefully. Once she has decided what she thinks about something, however, it is unchangable. The fountain pen becomes a very important symbol therefore for her character in the play and her unswerving commitment to her own ideas.