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Library Research: Search Techniques

Learn how to expand or narrow searches, use nesting, phrase searching, truncation and wildcards, proximity, and more

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How to conduct a search using Boolean operators or phrases.

Boolean Searching

To expand or narrow your searches, you will need to use a search technique called Boolean Searching.

What is Boolean Searching?

Boolean searching is a technique that combines keywords using connecting terms called Boolean Operators in an online search tool. The three basic Boolean Operators are AND, OR, and NOT.

Let's start with OR.

If you want to EXPAND your search and INCREASE your results, use OR.  A search for cats OR dogs will retrieve results that contain either cats or dogs or both.

All results containing cat, all results containing dog, and possibly results containing both, will be retrieved.

Illustration for Boolean Cats OR Dogs

If you are looking for information about dogs, an effective search would be: dogs OR canines OR puppies

This is effective because all of the keywords are synonyms or like terms for the same concept.

This use of OR effectively increases the number of results for that concept.


Some people might discuss dogs in their writing, but might refer to them using other terms, like canines or puppies. A search for just dogs might miss useful results that only contain the terms canines or puppies.

Now Let's look at AND*

Using AND will narrow your search.  A search for cats AND dogs will retrieve results containing both cats and dogs.

Illustration for Boolean Cats AND Dogs

The yellow rectangle, that contains BOTH the cat and dog pictures, represents the results.

*Most databases automatically put AND between search terms.


Boolean NOT is the operator that excludes results.

A search for dogs NOT cats would retrieve JUST results that mention dogs.  Results mentioning both dogs and cats would not be retrieved because cats have been excluded.

When should you use the NOT operator? Only when you are absolutely sure that certain terms need to be excluded. For example, when you need to exclude results that discuss another completely different meaning of a word, such as Saturn NOT car.

Be careful, because you could exclude something relevant if you use this too often!

Examples of Boolean Searches

Here are some examples of Boolean searches in the ERIC database.

dogs OR cats - a search designed to retrieve either dogs or cats

dogs AND cats - a search designed to retrieve BOTH dogs and cats

dogs NOT cats - a search designed to retrieve ONLY dogs

So, what does this mean?

  • Using OR retrieved the most results
  • Using AND retrieved the fewest results because results had to contain both cats and dogs.
  • Using NOT excluded those containing cats so that search retrieved fewer results than the search on dogs OR cats

Phrase searching

What do you do when you want to find a phrase like space shuttle Challenger?

Putting a phrase in quotes will tell the database to search for that exact phrase.

For example: "Space Shuttle Challenger"

This search will ONLY return items containing this exact phrase, and not items containing any of the words anywhere in the document.

If you searched for space AND shuttle, you could retrieve documents that mention space in one paragraph and shuttle in a completely different one. They could be far apart and unrelated.

Place quotation marks around phrases to search for them as exact phrases.

For example, a search for "systems theory" will retrieve documents that must mention systems theory as an exact phrase.

Longer names of articles, books, or journals, such as "Journal of health and human services administration" for example, would also be searched as complete phrases.

Nearly all databases, online catalogs, journal interfaces, and Internet search engines support quotation marks indicating phrase searches.

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