LitCharts assigns a color and icon to each theme in Moby-Dick, which you can use to track the themes throughout the work.
Limits of Knowledge
Fate and Free Will
Nature and Man
Race, Fellowship, and Enslavement
Madness
Religion
Summary
Analysis
Ishmael loops back to the beheading of a whale—something he has only glossed over in the previous chapters—to say that it is no easy business, and that Stubb, so skilled in it, was able to do it in about “ten minutes.” When the head is halfway hoisted and dragged behind the back of the boat, Ahab walks out to it and speaks directly to it, saying that, although the whale’s head is now silent, this head has also seen “deeper” in the ocean that any man, and that the head of the whale is in some sense the most ancient living part of all the living beings on earth—as old as Abraham himself. Ahab’s address to the head is interrupted by news from a sailor, that a ship has been spotted off the Pequod’s starboard side.
Ishmael seems to engage in a science common to the time—that of phrenology, or the study of the shape of heads under the belief that head-shape matched the shape of the brain beneath and the personality housed in that brain. This pseudoscience was soon debunked, but a common human impulse remains in contemporary brain-scans and similar technologies—the desire to understand what happens inside a man’s, or an animal’s, head, when we do not have direct access to that creature’s actual thoughts. Ahab, meanwhile, is moved by the mysteries the whale has seen.