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FHS-KE | Online Searching Techniques for Best Results: Boolean logic

Boolean logic i.e. Combining Boolean operators

Boolean Operators
Most databases and search engines support Boolean searching through their advanced search option. The 3 basic operators are:


  • AND – used to narrow search
  • OR – used to broaden your search
  • NOT-also narrows search. Using NOT before a keyword will exclude that keyword from the search. Best used when searching for a keyword with multiple meanings


  • medicine AND education
  • baby OR infant 
  • aspirin OR paracetamol
  • saturn NOT car
  • ulcer NOT stomach

One can choose to combine the Boolean Operators, for example:

  • (alcohol OR drug) AND abuse
  • Common cold AND (vitamin c OR zinc)


The Boolean operators can be illustrated using the Venn Diagram as follows:
(The gray shading represents the outcome of the Boolean operation) 

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Note: Some databases require the Boolean operators be in uppercase. Use the database help tips to confirm