What an index contributes

A book index appears to be a list of subjects and page numbers. Producing a useful one, however, requires decisions about meaning. A subject may be discussed without the word a reader expects ever appearing on the page. An indexer must recognize that discussion and choose an entry readers can find.

[A] Related entries can also be connected. [B] A general term may direct readers to several narrower subjects. [C] These links let people approach the same material with different starting vocabularies. [D]

Such decisions distinguish an index from a list of word occurrences. The latter can show where a particular expression appears, but it may omit relevant passages using other expressions and include passages where the word is only incidental.

An index necessarily reflects judgments about what matters in the book. This does not make it arbitrary: entries should be supported by the text and useful to its likely readers. Evaluating an index therefore involves trying meaningful searches, rather than merely counting how many entries it contains. A longer list may offer more routes, or it may bury important routes among unhelpful ones.