According to Peter Meyers, former associate publisher for O’Reilly Media’s Missing Manual series, indexes provide many benefits. A good index:

• includes concepts, not just words, enabling “thematic and concept-specific explorations” of the book
• provides “guided discovery”, by grouping related topics together, and using “see also” pointers
• helps “when you know what you want, but aren’t sure how to describe it”
• signals “depth of coverage” on a given topic, by including page ranges
• provides “a handy one-stop tally of coverage points throughout a book”
• helps prospective buyers sample the contents, in greater depth and detail than the table of contents.

I had a strict rule, which I think secret services follow, too: no piece of information is superior to any other.  Poser lies in having them all on file and then finding the connections.  There are always connections; you have only to want to find them.

Umberto Eco in Foucault’s Pendulum

And in such indexes, although small pricks To their subsequent volumes, there is seen The baby figure of the giant mass

Of things to come at large.

William Shakespeare in Troilus and Cressida

Where is the wisdom we have lost in the knowledge?
Where is the knowledge we have lost in the information?

T.S. Eliot in The Rock

There is no greater authorial sin than releasing a book without an index.  It should even be made an indictable offence.

S. R. Ranganathan in Library Book Selection

The savvy publishers are the ones who see indexing and access, not just content, as integral parts of their products.

Judy Luther in Outsell’s e-brief February 5, 1999

I have this thing about indexes.  If a book is well indexed, then that tells me something about the quality of its publishing.  If it doesn’t have an index, then I start thinking, “OK, who slapped this together?”

Lisa Guedea Carreño in Inc. Magazine. Jan. 1999

The ocean flows of online information are all streaming together, and the access tools are becoming absolutely critical.  If you don’t index it, it doesn’t exist.  It’s out there but you can’t find it, so it might as well not be there.

Barbara Quint, Editor, Search Magazine. 1994

Information seeking is a very complex human activity, not easily expressed in algorithms or calculations.  It is both cumulative and iterative, and needs to take into account such things as the seeker’s level of education, language preferences, and immediate goals.  So far, the best interface between a person and information has turned out to be another person – someone who has already studied the topic at hand.

Karen Coyle Wired, 1997

Though completeness is an ideal in any index, it is chimerical.  Doing an index is a lesson to end all lessons in the vagueness and subjectivity of human categories.  I have tried to compensate for inevitable lacunae and subjective mismatches with readers’ minds by indexing most major topics in several different ways.

Douglas R. Hofstadter in Le Ton beau de Marot: In Praise of the Music of Language

Obviously, in doing research I cannot read all of every important book, but I have made myself adept at reading indexes, a skill I recommend to would-be writers; I see in the indexes reminders of topics of which I am interested, but, of equal value, I see notations about ramifications that

had not occurred to me.

James A. Michener in The World is My Home

For the most part, the sorting routines employed in embedded indexing software do not conform to standard alphabetizing requirements of American publishers or national and international index standards.  The formatting capabilities of embedded indexing software are extremely limited.  The time required to embedded index entries and then edit embedded entries is much greater than the time required to perform the same tasks using other index-writing tools.

Nancy Mulvany in Indexing Books (1994)

The deficiencies, faults, and dangers of embedded indexing modules which are hawked by highly deceptive if not outright fraudulent slogans such as “with just a click of the mouse, you create back-of-the-book indexes!” …  These devices cannot produce an index, that is, a key to concepts dealt within a text, and their relationships to other concepts in that text.  They are designed by people whose idea of an index is an alphabetical list of words extracted from a text plus their locators.

Hans Wellisch in Indexing from A-Z (Second Edition, 1996)

“Some books live or die by their indexes.  An index can be the determining factor in whether a reference book is useful.  I have a cookbook that contains great recipes but has an index so eccentric that it is easier to memorize the recipes than to hunt for them.  On the other hand, I have just read a long biography packed with detail and possessing a marvelous index that enables the reader to locate any fact or incident with ease.  The Anglo-American tradition of serious writing and publishing calls for an extensive ‘scholarly apparatus’ (indexes, footnotes, citations, and bibliographies) and it is always a shock to read continental European, especially French, books that lack footnotes or indexes.  There have been a number of attempts to automate indexing, and there is no doubt that indexes have improved greatly over the last fifty years.  However, indexing cannot be mechanized and its largely anonymous practitioners need much flair and intuition to accompany the automated approach.  Pity the poor indexer!  Most readers take good indexes for granted and curse bad ones and, in either event, give little thought to the people who created them.  I will appreciate the work of the Unknown Indexer.”

Michael Gorman in Our Singular Strengths: Meditations for Librarians
(American Library Association, 1998)

What Is the Indexer’s Job?

• Identify and locate relevant information that the user might look for
• Distinguish substantial discussion and passing mention
• Provide terminology that may not exist in the text
• Analyze concepts to produce headings
• Direct the user, through cross-references, to appropriate terminology and concepts
• Group together references to the same topic
• Organize entries systematically, e.g., alphabetically

Why Are Indexes Needed for Electronic Publications Now That the Text Can Be Searched?

• With the advent of CD-ROMs and the Internet and their attendant search engines, many publishers and their technology advisers have sought to replace the functionality embodied by the indexes in their print products with various kinds of computer text searching software modules.
• What is missed by this approach is the re-utilization of a value-added asset, which the publishers have created and refined for many years. As noted above an index is a conceptual map of a publication.
• Search engines can only locate words or combinations of words – not concepts.  They can order the resultant hits by frequency or publication order – not by the conceptual hierarchy.
• Searching is a good use of technology but it should be an adjunct to, not a replacement for access to an index.  End users should be able to browse an index (or search an index) and then link, if possible, link to the appropriate text.
• Text searching is useful for finding very specific terminology (form numbers, names, terms of art, etc.)  But text searching is to reading an index as searching for materials in architectural plans is to finding books in a library using a card catalog.

An illustration:

Finding a bathroom in a building using an index is like using a floor plan, while using a search engine, it’s like checking each room to see if it has any porcelain.

David K. Ream