Boolean operators form the basis of mathematical sets and database logic.

• They connect your search words together to either narrow or broaden your set of results.
• The three basic boolean operators are: AND, OR, and NOT.

Why use Boolean operators?

• To focus a search, particularly when your topic contains multiple search terms.
• To connect various pieces of information to find exactly what you're looking for.
• Example:
  second creation (title) AND wilmut and campbell (author) AND 2000 (year)

Using AND

Use AND in a search to:

• narrow your results
• tell the database that ALL search terms must be present in the resulting records
• example: cloning AND humans AND ethics

The purple triangle in the middle of the Venn diagram below represents the result set for this search. It is a small set using AND, the combination of all three search words.

Be aware:  In many, but not all, databases, the AND is implied. 

• For example, Google automatically puts an AND in between your search terms.
• Though all your search terms are included in the results, they may not be connected together in the way you want.
• For example, this search:  college students test anxiety  is translated to:  college AND students AND test AND anxiety. The words may appear individually throughout the resulting records.
• You can search using phrases to make your results more specific.
• For example:  "college students" AND "test anxiety". This way, the phrases show up in the results as you expect them to be.

Using OR

Use OR in a search to:

• connect two or more similar concepts (synonyms)
• broaden your results, telling the database that ANY of your search terms can be present in the resulting records
• example: cloning OR genetics OR reproduction

All three circles represent the result set for this search. It is a big set because any of those words are valid using the OR operator.

Using NOT

Use NOT in a search to:

• exclude words from your search
• narrow your search, telling the database to ignore concepts that may be implied by your search terms
• example:  cloning NOT sheep

Boolean searching content by the MIT Libraries, CC BY-NC 4.0

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