Using Boolean Operators

Boolean operators were named after George Boole, a mathematician and the originator of algebra of logic (Boolean algebra) that became the basis for digital computer circuit design.

We use Boolean operators, also called connectors, in online search tools to connect our search terms so we can broaden (expand) and narrow (restrict) searches to increase the number of relevant search results we retrieve. The three most commonly used Boolean operators are AND, OR, and NOT.

Using Boolean operators between search terms lets us

and.gif

The Boolean operator AND is used to narrow (limit or restrict) searches. It limits the search results to items containing all the search terms connected with AND. Multiple terms can be combined with the AND operator to further restrict search results.

The image to the left illustrates the results of a search for "small group" AND decision-making. The purple shaded area represents the search results that would be retrieved -- only items with both search terms.

or.gif

The Boolean operator OR is used to broaden (expand) searches. It expands our search results to include items containing any of our search terms. Using the OR operator helps when we want to look for synonyms and alternative terms.

The image to the left illustrates the results of a search for "small group" OR decision-making. The purple shaded area represents the search results that would be retrieved -- any item containing one of the search terms.

not.gif

The Boolean operator NOT is used to narrow (limit or restrict) searches. It limits our search results by not retrieving items with the terms marked with NOT. The NOT operator should be used cautiously because it's easy to inadvertently exclude relevant material.

The image to the left illustrates the results of a search for "small group" NOT decision-making. The purple shaded area represents the search results that would be retrieved -- items with "small group" and no items containing the term decision-making.

NOTE: Some search tools require that Boolean operators be typed in all capital letters. Therefore, it is a good strategy to always capitalize them.

Boolean operators can be combined in many ways and used separately or together. Many search tools offer advanced search interfaces that let us choose Boolean operators from drop-down lists, as well as type them in search fields. These features give us quite a bit of control over our searches.

Watch a video about using Boolean operators created by The University of Auckland Library, NZ. This video explains what Boolean operators are and demonstrates using them in several different search interfaces.