Final answer:
In 'O Captain! My Captain!', Edgar Allan Poe uses symbols of the captain, ship, and journey to explore the theme of mourning for Abraham Lincoln's death and the end of the Civil War.
Step-by-step explanation:
In Edgar Allan Poe's poem, 'O Captain! My Captain!', the author uses the captain, the ship, and the journey as symbols to develop the theme of mourning for the death of Abraham Lincoln and the end of the American Civil War. The captain represents Lincoln, the ship represents the Union, and the journey represents the war. The poem expresses both the joy of victory and the grief of losing a beloved leader, emphasizing the sacrifice and loss experienced during this historical period.