Boolean Searching

Boolean searching is a way to improve search results.   Boolean terms are called "operators." 

• If your result set (number of items found or retrieved) is too large to read through productively, add another term or terms to your search to make the search more specific (using AND).
• If your result set has fewer items than you need, look over them.   Then add additional related or synonymous (having a similar definition) terms to broaden the search (using OR).

Boolean operators are AND, OR, and NOT [sometimes AND NOT or NO].  They can be combined in the same search.

AND narrows a search (more precise)

• usually results in fewer items than a search for either term
• for example: cookery and Italian

OR broadens a search (more inclusive; more items retrieved)

• can have up to the total of the two terms together
• for example: research or study

NOT/NO eliminates items.  (Some databases may have a different way to express this.)

• use NOT to eliminate homographical terms (words spelled the same but mean something different) and subcategories of topics that are not relevant
  • for example: Mercury not (god or element or planet)
    or, using a different combination of Boolean terms: Mercury and (automobile or car or vehicle)
  • for example: painting not watercolor
• Be careful: Mexico NOT New would eliminate items about Mexico the country that have the word "new" in the title found in such articles as "What's new in Mexico" and "Brave new Mexico."

Notes:

• It is not productive to go through search results of more than two or three hundred.  (An exception to this would be if you are working on a thesis, dissertation, or comprehensive research paper.) 
• If no more than 1 out of 10 of your retrieved items are relevant, narrow your search (AND).
• Some databases may use Boolean operators under a "Limit" or "Combine" function.

See Venn Diagrams for graphical representations of Boolean logic.

See Boolean Tutorial and Advanced Boolean Tutorial (each which take 3-5 minutes) for flash tutorials of this concept.

See also Conducting Electronic Searches (Online Writing Center) for an additional explanation, and examples of Boolean Searches on a few Web search engines.