Cetology of Moby-Dick

The cetology of Moby-Dick is Ishmael's zoological classification of whales. Although a work of fiction, Melville included sequences of chapters concerned largely with a pseudo-objective discussion of the properties of whales. The observations, based on a list of sources in addition to Melville's own experiences in whaling in the 1840s, include observations of various species from the order of Cetacea. These chapters are the most likely to be omitted in abridged versions of the novel.

Ishmael's observations are not a complete scientific study, even by standards of the day. Nevertheless, because of the general lack of knowledge about whales in the middle 19th century, the taxonomy in the novel provides a glimpse of the knowledge of whales by the whaling fleet and naturalists of the era.

Ishmael somewhat famously asserts in the novel that the whale is a "spouting fish with a horizontal tail". His use of the word "fish" here, however, is not meant a denial of the mammalian characteristics of the order Cetacea, but rather simply as an ad hoc definition as an animal that dwells in the sea. He attempts a taxonomy of whales largely based on size, based on his assertion that other characteristics, such as the existence of a hump or baleen, make the classification too confusing. Borrowing an analogy from publishing and bookbinding, he divides whales into three "books", called the Folio Whale (largest), Octavo Whale and the Duodecimo Whale (smaller), represented respectively by the sperm whale, the orca (which he calls the grampus) and the porpoise. Each such book is then divided into "chapters" representing a separate species.

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