Nonfiction, whatever form it may take, is built on a foundation of facts. Whether they present an account of actual events, as in family history or biography, seek to prove the validity of an argument, or demonstrate the correctness of a method of doing something, as in a how-to book, an author’s words are judged by the quality of the facts on which they are based. A nonfiction reader is likely to ask, “What’s the evidence for this?” Generally that evidence is based on documents, research, or accounts written by others and used by the author. So it behooves the nonfiction author to include references to allow the reader to know and evaluate the quality of the sources from which that evidence is drawn.
The choice of what documentation and references to use in a nonfiction book is often based on the book’s intended audience. An author writing in an academic style – a historian, scientist, or economist – must meticulously document the sources of each of the facts they present by including both very precise, complete source notes and a full bibliography. This allows the reader to judge the factual basis of the book’s premise. An author writing for a more general audience may choose to include a summary of the sources he or she used in creating the book. A more narrative-based book might employ even briefer notes on only the most important sources.
When self-publishing a book, space is also a consideration in deciding how extensive the sourcing should be. The length of a book is an important consideration in determining the cost of printing. Some cost-conscious authors now condense the source notes in a printed version of the book and provide more complete notes online for those who check every detail.
In deciding what to include it is best to remember that an index, after the table of contents, is the finding aid most likely to be used by readers. Particularly in books that will be used as references, a good index is essential.
If you decide to include source notes, your book designer will tell you that endnotes are preferable to footnotes because they don’t interrupt the flow of the text, thus making it more readable.
Finally, whatever source information you provide should be formatted using a good style guide. The Chicago Manual of Style, The Associated Press Stylebook, and the MLA Style Manual are the preferred choices. Some disciplines, like family history, have specialized guides like Elizabeth Shown Mills Evidence Explained, but they are often based on Chicago style. The important thing is that these guides will help you cite your sources correctly which adds a tone of professionalism and veracity to what you say in the book’s text.