How to Search the Web

What Is a Boolean Search?

Named after 19th-century British mathematician George Boole, a Boolean search allows you to specify the logical relationships among keywords in your search. The basic elements of a Boolean search involve specifying whether keywords or phrases can appear in a search, must appear in a search, or must not appear in a search. By specifying these relationships, you are better able to locate information relevant to your topic.

The most commonly used Boolean search terms are AND, OR, and NOT. Please note that, while these are the terms most often used, many search engines use their own variants of these terms on advanced search forms. It's also important to remember that the specific commands for requiring or excluding keywords or phrases will vary depending on the electronic source you are searching. Your best bet is to review the online help on Boolean searches when you're searching a database, library catalog, or Web search site for the first time.

Boolean AND Searches: When you conduct a Boolean AND search, you tell the search engine to locate all records containing one keyword and another (that is, all records the search engine returns must contain both words, not just one of them). For example, if you search for all records containing the keywords education AND reform, you'll obtain a smaller, more focused number of results than you would by searching for just one keyword or the other.

Search For: education AND reform

Result: all records containing both keywords education and reform

Boolean OR Searches: When you conduct a Boolean OR search, you tell the search engine to locate all records containing one keyword or another (that is, all records the search engine returns must contain at least one of words but not necessarily both). For example, you could search for all records containing the keywords publisher OR press. This allows you to obtain a larger number of results than you would by searching for just one keyword or the other.

Search For: publisher OR press

Result: all records containing either or both of the keywords publisher or press

Boolean NOT Searches: When you conduct a Boolean NOT search, you tell the search engine to locate all records that do not contain a particular keyword. For example, you could search for all records containing the keywords composition but NOT music. Because the term composition is used in both writing and music instruction, if you're interested in looking only for sources that deal with written composition, you can use the Boolean term NOT to exclude sources dealing with musical composition.

Search for: composition NOT music

Result: all records containing the keyword composition but not containing the keyword music

Complex Searches: You can also use Boolean search terms in combination to construct complex searches. For example, you could search for all records containing the keywords writing or composition and the keyword computers but not the keyword music:

Search for: writing OR composition AND computers NOT music

Result: all records containing the keywords writing or composition and computers, but not containing the keyword music