A mathematician named George Boole studied the logical relationships of the words AND, OR, and NOT, and most databases use this logic as the basis of their searching (thus the name “Boolean” for this system).  Boolean searching uses AND, OR, and NOT to combine two or more terms; databases are more precise than Google, which allows you to type in a string of terms. 

Connecting the key words or concepts with the Boolean operators AND, OR, and NOT get you much better results by expanding or limiting your options.


It works like this:  AND is used when you want information about two or more topics, and you want all the terms to be covered in the same article.  You’re narrowing your results to articles where your terms overlap.

NOT also narrows results, but it’s used to exclude a term from your results, not include it.  OR expands results by providing all of the articles on all the terms you link with OR.

The screenshot walkthrough below gives you a visual idea of how they each work.  You can use more than one in combination to create a string of key words connected by Boolean operators.

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  • 1.  Know the difference between AND, OR, and NOT.
    •  Know which one expands searches and which ones narrow them, and why.
    • Know when to use which term.
  • Be able to conduct a Boolean search combining two terms.
  • Be able to conduct a Boolean search combining three terms.

Video Tutorial

Screenshot Walkthrough

1.  The three Boolean operators are AND, OR, and NOT.  Doing a search for each one gets you the blue section of results.  AND looks for the overlap between two or more terms–it narrows results.  OR looks for both terms, separately or together, and returns everything–it expands results.  NOT exlcudes a term completely even where they overlap–it also narrows results.



2.  Linking terms with AND returns articles where both terms are included in the article.  The narrows results because both terms must be there.



3.  Linking terms with OR returns articles where either term is mentioned–either global warming OR climate change, for instance.  It expands results because as long as one term or the other is in the article, even if they don’t overlap, it lists the article.


4.  Linking terms with NOT narrows results by excluding terms.  In this example, I excluded greenhouse.  This takes out all results that mention greenhouse gases or the greenhouse effect.


5.  You can combine more than two terms and use more than one Boolean operator at a time.  Boolean operators search in a specific order: NOT first, then AND, and lastly OR.  Keep this in mind as you search since it can change the results.



Further Practice

Want some practice?  Try this case scenario:

Your mission, should you choose to accept it: to do a search for articles on drug use in horse racing or dog racing.  This is your chance to practice doing a real search using what you’ve learned.  Don’t worry about your database choice—use Academic Search Premier.  Focus instead on what your search terms are and how to combine them properly.

To ponder:  What did you come up with?  Were your results relevant and on-target, or did you combine the terms the wrong way?  Boolean searching can take some practice, so don’t be afraid to experiment and come up with lots of combinations to test.

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