Boolean Logic is a system of rules (or commands) to express the relationship of two or more concepts. The most commonly used commands (also called operators) -- AND, OR, and NOT -- can be used to link search terms or narrow search results. The correct use of Boolean operators in a search, whether it be in a search engine (Google), a library catalog, or a research database will produce more relevant and reliable results.
- AND: used in order to require that all search terms be present on the web pages listed in results. For example, you may want to find pages referencing both rules and laws.
- You use the command like this: rules AND laws
- Since AND is the default operator in search engines (like Google), it is unnecessary to type it. For example, you can type rules laws and your results will retrieve pages that include both rules and laws on the same page
- OR: used in order to allow any of the specified search terms to be present on the web pages listed in results. For example, you may want to find pages that contain either of the words America or U.S.
- You use the command like this: rules OR laws
- Will broaden your search and increase the number of results. Note that OR works only in upper case between search terms in Google.
- NOT: used in order to require that a particular search term NOT be present on web pages listed in results.
- In a library catalog or research database, you use the command like this: plants NOT trees
- In Google, you must use the minus sign (-) without spaces. Example: plants-trees