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 describes the “forehead” of the sperm whale, or the space between the eyes, which has no features other than small indentations and wrinkles in the whale’s skin. Ishmael wonders, aloud, if there is a man of learning who can “read” the wrinkles of the whale’s head, the way that some scientists are believed to be able to read the bumps in human skulls (via “phrenology”). Ishmael states that he is not capable of reading the sperm whale’s forehead—nor the thoughts of the whale—but he presents this information to the reader, to make of it what he or she can.
Another instance of phrenology, this time explicit. Ishmael clearly wishes to bore into the minds of all those he describes—of Ahab, of Queequeg, of Moby Dick itself. But Ishmael seems to know that it is equally difficult or even impossible, for different reasons, to describe the thoughts of any of these. Ishmael seems to realize that the task of the writer is to imagine oneself into the consciousness of another, be they human or animal.