Boolean logic consists of three logical operators:

• AND
• OR
• NOT

• This search will retrieve records in which AT LEAST ONE of the search terms is present. 
• The shaded circle with the word college represents all the records that contain the word "college" and the shaded circle with the word university represents all the records that contain the word "university."
• OR logic is most commonly used to search for synonymous terms or concepts.

• The more terms or concepts we combine in a search with OR logic, the more records we will retrieve.

• This search will retrieve records in which BOTH of the search terms are present.
• The shaded area is the overlap of the two circles representing all the records that contain both the word "poverty" and the word "crime."
• Note: records with only "poverty" or only "crime" are not retrieved.

• The more terms or concepts combined in a search with AND logic will retrieve  fewer records. For example: 

• This search retrieves records in which ONLY ONE of the terms is present.
• The shaded area with the word cats represents all the records containing the word "cats."
• No records are retrieved in which the word "dogs" appears, even if the word "cats" appears there too.

 

Search terms	Results
cats	3,651,252
dogs	4,556,515
cats NOT dogs	81,497

Using Boolean Logic when Searching on the Internet

1. Full Boolean logic with the use of the logical operators
2. Implied Boolean logic with keyword searching
3. Predetermined language in a user fill-in template

1. Full Boolean logic with the use of the logical operators

This is an option offered by many search engines. For example:

Query: I need information about cats.
Boolean logic: OR
Search: cats OR felines

Query: I'm interested in dyslexia in adults.
Boolean logic: AND
Search: dyslexia AND adults

Query: I'm interested in radiation, but not nuclear radiation.
Boolean logic: NOT
Search: radiation NOT nuclear

Query: I want to learn about cat behavior.
Boolean logic: OR, AND
Search: (cats OR felines) AND behavior
Note: Use of parentheses in this search is known as forcing the order of processing. In this case, we surround the OR words with parentheses so that the search engine will first process this part of the search. Next, the search engine with combine this result with the last part of the search. Using this method, we are assured that the OR terms are kept together as a logical unit.

2. Implied Boolean logic with keyword searching

Keyword searching: to search you enter terms representing the concepts you wish to retrieve. Boolean operators are not used.

Implied Boolean logic: symbols are used to represent Boolean logical operators. On the Internet the absence of a symbol is  significant, as the space between keywords defaults to either OR logic or AND logic. Many well-known search engines, such as AltaVista (main screen), Excite, Infoseek, and MetaCrawler, default to OR.

For example:
Query: I need information about cats.
Boolean logic: OR
Search: cats    felines

The space between the keywords is interpreted as the Boolean OR. 

Query: I'm interested in dyslexia in adults.
Boolean logic: AND
Search: +dyslexia    +adults

Query: I'm interested in radiation, but not nuclear radiation.
Boolean logic: NOT
Search: radiation    -nuclear

Query: I want to learn about cat behavior.
Boolean logic: OR, AND
Search: cats    felines    +behavior

This page is based on a more comprehensive page created by the University of Albany Library's Boolean Primer