In his beautiful poem titled "O Captain! My Captain!," poet Walt Whitman likens Abraham Lincoln to the captain of a ship and his government to a ship through what is actually a very famous metaphor created by Plato, referred to as the metaphor of Ship of State.
In Book VI of the Republic, Plato constructs the metaphor of Ship of State to describe what it means to govern a city-state. Plato compares governance to mastering a naval ship and argues only "philosopher kings" have what it takes to be capable of captaining such a ship. A "philosopher king," defined by Plato is simply a king, or leader, who is also a philosopher. A philosopher, to Plato, was one who loved truth and the pursuit of knowledge to the extent that every aspect of his/her day-to-day life was a pursuit of the true forms of Virtue, Beauty, and the Good. Since these are the only pursuits of a philosopher, a philosopher refrains from the immoralities that drive other leaders, such as kings, to act corruptly and abuse their powers. In addition, philosophers are not born politicians; they are born thinkers. Since they are not born politicians, they have no desire for authority in the same way that politicians often strive only to seek authority. Plato argues that the best leader is one who has no true desire to be a leader because only those sorts of leaders can be trusted to be humble enough to refrain from abusing their powers. Therefore, according to Plato, only a philosopher king can be trusted to guide and steer a government in the same way that a captain guides and steers his naval ship.
Hence, in using Plato's famous metaphor of a Ship of State captained by a philosopher king, Whitman is likening Lincoln to a philosopher king and likening Lincoln's government to the utopian government that can be achieved through the rule or a philosopher king. Lincoln can be likened to a philosopher king due to evidence of his extensive wisdom, his pursuit of self-education, his mercy, and his determined pursuit of liberation. His wisdom and pursuit of liberation can be seen in the famous words of his speeches and letters, such as in the letter he wrote to Republican Representative Henry Pierce, April 6, 1859:
This is a world of compensations; and he who would be no slave, must consent to have no slave. Those who deny freedom to others, deserve it not for themselves; and, under a just God, can not long retain it.
Aside from likening Lincoln to a philosopher king captaining the Ship of State, Whitman also uses strong imagery to capture the country's feelings about the loss of Lincoln. Images of bells tolling, flags waving, and of bouquets and wreaths being given help capture the feeling of triumph at having won the Civil War and freed all the slaves. In addition, the image of "shores a-crowding," meaning crowded shores, depicts the masses of supporters gathered to see Lincoln and cheer him on but who are soon devastated by his death.