Boolean operators are words and symbols, such as AND or NOT, that let you expand or narrow your search parameters when using a database or search engine. When you search using these operators, it is known as a Boolean search.

You can use Boolean operators such as AND, OR, and NOT alongside keywords to create a Boolean string that will refine your search to find the most relevant results and sources.

How to use Boolean operators

Knowing how to use Boolean operators effectively can save you a lot of time and help you to find useful sources, determine the relevance of your research topic, and create strong research questions. It’s also very helpful when you’re working on a literature review or systematic review.

AND

AND will provide search results containing both or all of your keywords.

Use this when you want results that contain two or more specific keywords.

OR

OR will provide search results containing at least one of your keywords.

Use this when you want results that contain at least one (though not necessarily both) of your chosen keywords.

NOT

NOT will provide search results containing the first of your keywords but not the second. Make sure to put your keywords in the correct order when using NOT, as the search results provided will exclude the latter keyword.

Use this when you want results that contain one specific keyword but not another.

Parentheses: ()

Parentheses allow you to group together keywords and control the order in which the terms will be searched, just like in a mathematical statement. Keywords and Boolean operators within parentheses will be searched first, followed by keywords outside parentheses.

For example, the combination shown below will provide results that are initially filtered to contain at least one of “id” or “ego,” and then further refined to also include “developmental.”

You can also use more than one pair of parentheses. The search will filter results based on the innermost parenthetical keywords first, followed by the keywords in outer parentheses, and finally the keyword(s) outside parentheses.

Quotation marks: “”

Quotation marks will provide search results containing the exact keyword(s) contained within.

Use this when you want results that contain a precise keyword or keywords.

Asterisk: *

An asterisk will provide search results containing variations of a root word.

Use this when you want results that contain the keyword that you entered or other words that begin with those letters.

Each database or search engine may use Boolean operators in slightly different ways. Therefore, it is important to check how Boolean operators work in the particular database or search engine you’re using.

Note: Many databases and search engines also offer an “advanced search” option that lets you choose the most relevant Boolean operators from a drop-down list, like in the example from JSTOR below.
 

Proximity operators

Proximity operators are similar to Boolean operators. They let you filter results based on the proximity of one keyword to another.

Proximity operators include NEAR (Nx), WITHIN (Wx), and SENTENCE.

Note: Not all databases use proximity operators. Be sure to check the search operations of the database you are using.