Boolean operators

Boolean operators form the basis of mathematical sets and database logic. They connect your search words together to either narrow or broaden your set of results. The three basic Boolean operators are: AND, OR, and NOT.

Use “AND” in a search to:
  • narrow your results
  • tell the database that ALL search terms must be present in the resulting records

For example: cloning AND animals AND ethics:

Use “OR” in a search to:
  • connect two or more similar concepts (synonyms)
  • broaden your results, telling the database that ANY of your search terms can be present in the resulting records

For example: Tinder OR “mobile dating”:

Use “NOT” in a search to:
  • exclude words from your search
  • narrow your search, telling the database to ignore concepts that may be implied by your search terms

For example:  students NOT “pre-school students”

Databases usually recognize AND as the primary operator, and will connect concepts with AND together first. If you use a combination of AND and OR operators in a search, enclose the words with OR together in parentheses: students AND (facebook OR “social media”). In many databases you may use the advanced search form to build up your search with drop-down menu (see the examples above). Write all the Boolean operators in CAPITAL LETTERS.

Watch a video “Using Boolean operators” (2:14) by John M. Pfau Library:


Licence: CC BY 4.0

(5/2017 RH)