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Developed by the English mathematician George Boole, Boolean is a system of logic statements, known as operators, that compare relationships between two or more words, statements, or other variables, to determine whether or not the overall statement is true. The most common operators are AND, OR and NOT.
Boolean logic has become the basis for many programming languages as well as computer database searches. They allow users to narrow or broaden the scope of results based on the relationship between two more variables.
For example, if you are researching commonalities between world wars, you want to narrow your search to just results that mention both wars. In this case, you could use the Boolean operator AND: “World War I” AND “World War II”.
Also See: Advanced Web Searching
Frequently Asked Questions
Can I use more than one Boolean operator in a search?
Yes. You can include as many operators as necessary within a search. If you need to create complicated statements, you can also use parenthesis, similar to the way you would when creating a complex mathematical equation. See our Advanced Web Search article to learn more.
Can I use Boolean expressions in search engines?
Many search engines allow for the use of Boolean expressions; however, each search engine has its own specific way of handling operators. In most cases, the search engine will include the AND operator default, providing results for articles that contain every word you enter. If there are a limited number of results, the search engine may include articles that do not contain one or more words, but they will typically advice you of this adjustment.
Some search engines allow users to include a + sign before words that must be contained in the results, or a – sign before words that should not be included in the results. For more information on the specific uses of Boolean expressions allowed, check with your search engine’s help system, which can usually be found at the bottom of the search service’s homepage.
Can I limit search results without knowing the appropriate Boolean operators?
Many search engines offer an advanced search option, which allows you to limit your results. In most cases, these advanced options are performing the same functions as Boolean operators. They may include an option to require all words to be displayed (which mimics the AND operator), any of the words entered (performing the OR function), or a “none of these words” option to exclude certain words from your results (the NOT function). Most people find these advanced search pages easier to use than complex Boolean expressions, because they provide detailed explanation for each rule, but you can often accomplish the same thing using Boolean expressions.