Frequently asked questions 3 – Combining search terms


  • What is the meaning of AND, OR and NOT in searching?
  • What is Boolean logic?
  • How do I use my search terms in a database?

Boolean logic organizes concepts together in sets. When searching databases or online catalogs, these sets are controlled using Boolean operators OR, AND and NOT.

Use OR to combine synonyms, close terms and alternatives.

For example:

  • newborn OR neonate
  • sepsis OR “blood poisoning”
  • running OR jogging

Though it seems very simple, it is sometimes confusing, as Boolean OR is actually AND-OR, meaning either-or or both.


Use AND to limit the search to only those results that have all the terms combined with AND.

For example:

  • newborn AND diabetes
  • running AND “knee injuries”
  • sepsis AND “intensive care”


If you need both OR and AND, use brackets to combine the sets logically.

For example:

  • (newborn OR neonate) AND diabetes

Use NOT to exclude terms.

For example:

  • newborn NOT premature
  • running NOT sprint
  • sepsis NOT severe


Watch a short video!

Boolean logic is named after the nineteenth-century mathematician George Boole.


By: Tuulevi Ovaska, Head of Services, Kuopio University Hospital Medical Library, University of Eastern Finland Library