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Skills at Library Essentials

Guides to search skills and using library research resources

Combining search terms

Using Boolean operators

What are Boolean operators?

Boolean operators are words you can use in your search to combine or exclude keywords from your results.

The three main Boolean operators are: AND, OR, NOT.

Why use Boolean operators?

Boolean operators will make make your search more focused, and give you more relevant results. You can use them to either expand or limit your search, as described below. 

AND narrows your search.

Combine your keywords with AND to make sure that they all appear in your search results. Venn diagram A AND B

For example, searching for 'fake news AND media' will make sure your results contain both of these words. The more keywords you add with AND, the narrower your search will be, and the fewer results you will get. For example we could add to this search to look for 'fake news AND media AND elections'. 

In some databases, the search will imply AND between keywords automatically. However, this doesn't apply to all databases, and for clarity and to make sure you're getting the best possible results, it is best to use the AND operator between keywords. 

OR broadens your search.

Use OR between your keywords to include any or all of them appear in your results. Venn diagram A OR B

You can search for alternatives and synonyms at the same time by using OR. This will broaden your search and give you a larger number of results. It will also save you time, as you won't have to run separate searches with your synonyms, you can search for them all at once. 

For example, you could search for 'football OR soccer' to find results related to the sport, regardless of how it has been described by the author. You could also use it to search for acronyms, such as 'genetically modified organism OR GMO' or for alternative spellings such as 'colour OR color'. 

NOT narrows your search. 

NOT is used to exclude keyword(s) from your search. Venn diagram A NOT B.

If you are getting lots of irrelevant results, and there is a certain keyword you do not want to see in your results, you can try excluding it with NOT. However, proceed with caution, as you don't want to miss out on any useful results!

For example, you could search for 'media NOT radio' or 'fish NOT freshwater'. 

Order of search terms

When combining your search terms, be aware of your search order. 

Particularly when you are building complex searches with multiple keywords and Boolean operators, you will need to be careful so that you can get the results you want. 

Databases will usually process Boolean operators in order, with AND first. So, any keywords linked with AND will be processed first, before those with OR. If you are using a combination of AND and OR, use parentheses (brackets) to group your keywords together to make sure they are processed in the correct order.

Use parentheses around your synonyms, alternatives or related terms combined with OR to keep them together. 

For example: 

We are searching for social media or fake news in relation to elections. We can search for "social media" OR "fake news" AND elections* and, depending where we use parentheses, we can get very different results. The results numbers given are from a search in the database Web of Science. 

* In this search we have kept the phrases "social media" and "fake news" together by putting them in quotation marks. This is called phrase searching, and you can find out more about this on our Top Search Tips page.

 Search 1: ("social media" OR "fake news") AND elections

1,359 results. Venn diagram ("social media OR "fake news") AND elections

Results will contain the following combinations: 

  • social media, elections
  • fake news, elections
  • social media, fake news, elections 

 Search 2: "social media" OR ("fake news" AND elections)

47,288 results. Venn diagram "social media" OR ("fake news" AND elections)

Results will contain the following combinations: 

  • fake news, elections
  • social media, fake news, elections
  • social media

In this search you get many more results. You will also find that some of the results include social media, but none of our other keywords, so they may not be related to our topic at all. 

Search 3: "social media" OR "fake news" AND elections

47,288 results. Venn diagram "social media" OR "fake news" AND elections

This search will give the same results as Search 2, because of how the search has been processed. Precedence has been given to the keywords combined with AND. 


Boolean operators video