Answered By: Ask a Librarian
Last Updated: Feb 24, 2020    

Boolean operators are used to combine words or phrases selected for a search when searching a retrieval system, e.g. online catalogue. There are three operators frequently used in search systems and software:


These operators can help you to narrow or broaden your searches when been appropriately used.



Usually, there will be more than one concept in a topic. How can you retrieve articles which are the most relevant to your topic then?

Boolean “AND” can help to narrow your search results by combining search terms. Using “AND” between keywords means that both terms must appear somewhere in the record.


Imagine that you are searching on the topic “the impact of poverty on child education”. You have picked up “poverty” and “child education” as your search terms. You should use “AND” to combine the two terms.

Search statement: Poverty AND Child education

Results: Resources containing both “poverty” and “child education” (the green shaded section)



What if your search statement returns only a few results and they are not enough for your research?

Use Boolean “OR” to combine some synonyms or related terms which are developed by you as search terms, and you can get more search results. The search terms which are combined using “OR” will all have chances to be retrieved, which means “OR” helps to retrieve records containing either one or some or all the terms.


Your target study population is teens.

“Juvenile” is a synonym of “teen”. If you wish to find more relevant resources, you can combine them using “OR”.

Search statement: Teen OR Juvenile

Results: Resources containing either “teen” or “juvenile” or both of them (the green shaded section)



What if your searches retrieve unwanted resources?

Use Boolean “NOT”.

Boolean “NOT” limits a search by restricting the terminology which are searched for.


Let’s say that you only wish to find resources about children but not adults. In order to look into the specific population, you may use “NOT” in your search statement.

Search statement: Children NOT Adults

Results: Resources containing “adults” will be excluded in the search results.