When describing Druse’s experience in the Union army up until this point, the narrator uses alliteration, as seen in the following passage:
By conscience and courage, by deeds of devotion and daring, he soon commended himself to his fellows and his officers; and it was to these qualities and to some knowledge of the country that he owed his selection for his present perilous duty at the extreme outpost.
The alliteration here is in the first part of the sentence, when the narrator starts several words with /k/ and /d/ sounds when describing how “by conscience and courage, by deeds of devotion and daring, [Druse] soon commended himself to his fellows and his officers.” These sounds show up in more subtle ways in the rest of the passage in words like “country” and “duty.”
Bierce intentionally uses alliteration at this point in the story in order to highlight Druse’s heroic behavior. This stylistic choice adds a romantic quality to the language that matches the dramatic content of the words, helping readers understand just how courageous and daring Druse is as a soldier and as a man.
This moment is also an example of situational irony. As the alliterative part of the passage communicates, Druse is a brave and skilled soldier, recognized as such by “his fellows and his officers” alike. Ironically, he ends up being punished for his bravery by being selected for his current “perilous duty at the extreme outpost.” Here, Bierce highlights the ludicrous nature of war—there is no escaping its horrors, even for the most courageous and daring soldiers.
That Druse decides to kill his father after recalling words of advice that his father gave him makes his father’s death an example of situational irony. While readers might assume that Druse would honor his father by not killing him, he instead honors the man by taking his words about duty to heart.
The following passage captures how Druse ironically justifies killing his father using his father’s own words:
Druse withdrew his eyes from the valley and fixed them again upon the group of man and horse in the sky, and again it was through the sights of his rifle. But this time his aim was at the horse. In his memory, as if they were a divine mandate, rang the words of his father at their parting: “Whatever may occur, do what you conceive to be your duty.” […] Duty had conquered; the spirit had said to the body: “Peace, be still.” He fired.
Immediately before this passage, Druse is unsure about whether to shoot the horseman or not and even tries to talk himself out of it, thinking that perhaps the man hasn’t seen the Union troops in the valley and therefore isn’t a threat. It is only when he remembers the “divine mandate” his father gave him “at their parting” that he decides to shoot. As his father said, “Whatever may occur, do what you conceive to be your duty.” And, ultimately, Druse decides to fulfill his duty as a Union soldier fighting for a more progressive future rather than his duty as a faithful son.