Sometimes, a simple keyword search finds just what you need.
But...keywords could appear anywhere in the book's record. For example, searching with the keyword "dog" would bring back not only books with dog in the title, but also the table of contents and the publisher, e.g., Bird Dog Publishing and Bottom Dog Press. The item published by Bottom Dog Press may have nothing to do with what you are looking for.
This will not be the case with a subject heading. A subject heading indicates that that topic is a major part of the work.
If you rely only on keyword searching, you may miss some excellent, relevant sources since keywords, like the tags applied to photographs, are not standardized.
Searching by subject, on the other hand, allows you to tap into a system of standardized, controlled, and organized vocabulary and thus more precise and comprehensive searching.
standardized, controlled, and organized vocabulary and thus more precise and comprehensive searching.
An example: If you were searching for information on "space," as in space travel, the solar system, etc., a keyword search using the term "space" would yield many results about living space, architecture, and other irrelevant results. In addition, you'd miss quite a few relevant sources since the subject term for space is "astronomy."
Click astronomy to see a browsable list of sub-categories and related terms.
If you're looking for creative nonfiction works in the catalog, "creative nonfiction" is actually not a the best term. But you can use the keyword phrase "creative nonfiction" to get to some better, more fruitful terms.
Libraries/librarians use non-intuitive language to organize books, but this language is helpful in finding the books you need: