“The Sisters” is a modernist short story. Joyce was a leader of the Modernist literary movement, which arose out of writers’ frustrations with traditional literary conventions. Rather than telling adventurous or inspiring stories with clear resolutions, modernist writers zeroed in on the alienation they saw around them in the industrialized modern world. This often led to stories with experimental structures, unsettling moods, and ambiguous endings.
Many of these features appear in “The Sisters.” For example, Joyce never directly addresses the medical condition that led to Father Flynn’s death. Some scholars believe that the story insinuates that he died from syphilis (thus explaining his paralysis and other symptoms), while others are not so sure. What's more, Joyce hints throughout the story that Father Flynn may have been a pedophile, but the characters never say this aloud—instead, the idea is only hinted at through evasive statements full of ellipses. This sort of ambiguity—which leaves readers to draw their own conclusions—is a classic component of modernist writing.
The abrupt ending with no clear conclusion also makes this story quite Modernist. Readers are left wondering how they are supposed to feel about Father Flynn and about the Catholic Church as a whole. The women in the story don’t seem to be moral guides, but the men don’t seem to point the way either, as they believe an appropriate replacement for Catholic education is the mere act of physical exercise. This modernist ending forces readers to come to their own conclusions about how the narrator should move forward from here.