Boolean operators are specific words used to combine keywords to improve the chances of finding relevant information.
The most commonly used Boolean operators are AND, OR and NOT.
Boolean Operator |
Purpose |
Example |
Result |
AND |
combine keywords that reflect different concepts |
humour AND therapy |
Search results will contain both of the terms humour and therapy. Using AND decreases the number of results, because each time a keyword is added, the focus of the search is narrowed. |
OR |
combine keywords that reflect similar concepts |
humour OR laughter OR comedy |
Search results will contain one, or both, of the terms humour or laughter or comedy. Using OR increases the number of results, because a broader range of keywords is searched. |
NOT |
exclude a keyword |
humour AND therapy NOT children |
Search results will contain both of the terms humour and therapy but only if they do not contain the third term children. Using NOT reduces the number of results by excluding information not required. |
Using Boolean operators when searching the Library Catalogue, databases and the Web, can help with retrieving relevant information results.