Boolean Logic

Introduction

When searching for information, you want to establish the relationship between your ideas (that is, you want the database to understand that you want articles that have information both about Alexander Hamilton AND Thomas Jefferson). To do so, you would use Boolean operators which are: AND, OR, NOT. Use these operators to combine terms when searching in electronic databases and search engines.

Each database and search engine uses slightly different commands for combining terms. Always refer to the help screens of the database or search engine that you are using before beginning your search!

AND

AND retrieves documents that contain both or all of your search terms. AND is a good way to narrow down your search by limiting results to the most important ideas.

Picture of two circles intersecting. One is labeled A. Hamilton and the other is labeled J. Madison.

The database will search for articles or books that contain information both about Alexander Hamilton and James Madison.

Variations: Some search engines use an ampersand (&) for AND. Also, the plus sign (+) is often considered to be interchangeable with AND. There is, however, a subtle difference: the plus sign requires a word to appear. If you type in president +Clinton, you will retrieve all the documents containing the word Clinton, but they may not all include the word president. To get both words, you would type +president +Clinton.

Examples:

Example of using one keyword.

Example of using one "AND" with one other keyword.

Example of using two "ANDs" with three total keywords.

Note the amount of results in the upper left corner of the results box in each example. Every time an "AND" with a new keyword is used, the narrower the results.

OR

OR retrieves documents containing any of the terms you enter, but not necessarily all:

Picture of two circles intersecting. One is labeled fruits and the other is labeled veggies.

As the diagram shows, looking for articles using the terms fruits OR veggies will bring back articles with either word or both in them. OR is often used to broaden a search such as:

  • assisted suicide OR euthanasia
  • bikes OR bicycles
Examples:

Example of using one keyword.

Example of using one "OR" and a synonym.

Note the amount of results in the upper left corner of the results box in each example. After adding an "OR" the results grew.

NOT

NOT retrieves documents excluding certain search terms:

Picture of two circles intersecting. One is labeled Calvin and the other is labeled Klein.

Calvin NOT Klein will find documents including information about John Calvin but not about the fashion designer. NOT is often used to make sure that term confusion, especially around individuals with similar names or concepts with similar names, are removed. You can also use NOT to remove terms you are often seeing appearing in search results. Example: cognitive psychology NOT science

Variations: Some search engines use NOT, and some use a different symbol, such as an exclamation point (!), as a symbol for NOT. The minus sign (-) can also be used in some search engines to eliminate unwanted words (e.g., Calvin -Klein).

Examples:

Example of using one keyword.

Example of using "NOT" with one other keyword.

Note the amount of results in the upper left corner of the results box in each example. After adding a "NOT" the results narrowed.