LitCharts assigns a color and icon to each theme in A Horseman in the Sky, which you can use to track the themes throughout the work.
Duty, Morality, and Justice
Sons vs. Fathers
The Horrors of the Civil War
Summary
Analysis
Carter Druse, having taken his shot, reloads and carries on his sentry duty, never having gotten up from his position. After ten minutes pass, the sergeant crawls up next to Druse and presses him for information. Druse tells him that he shot a horse off of the cliff and when it died it went over the edge. Druse’s face is white, but shows no emotion. When the sergeant inquires who was on the horse, he reveals that it was Druse’s father.
With the revelation that the horseman whom Druse was deliberating on killing was his own father, the entire story changes. Bierce forces the reader, who has already taken one journey of moral deliberation, reconsider all that they have just read in the light of this tragic, even horrific, new circumstance.