Smooth Operators
Boolean operators (AND, OR, and NOT) help you broaden or narrow your search, depending on which operator you use. Each operator works according to its own set of rules to affect how your keywords are searched. Boolean operators act on the keywords around them in a way similar to how math operators act on numbers. Note that in many finding tools, you must capitalize Booleans for them to be recognized.
AND
AND specifies that all the keywords you connect with AND must be present in your search results. The more search terms you add with AND, the more you will restrict your results, and the fewer results you will get. AND is most useful when you have two or more keywords and want to make sure all are included in each of your search results.
Let’s say you’re doing research on the evolution of dogs. Here is an example of a Boolean search you might try. The blue shaded area represents dogs AND evolution:
By constructing your search with AND between each term, your results would each need to contain both dogs and evolution. Any item with only one of those terms but not the other would be excluded from your results. This is useful because the majority of sources about dogs do not talk about evolution, and the majority of sources about evolution do not talk about dogs specifically.
You can use more than two keywords with AND, but be careful not to go too far. Adding too many terms may overly restrict your results. If you get zero results in a search, that doesn’t necessarily mean that there isn’t any information on your topic. You may just need to change the ways you combine your search terms (or which terms you use) and try again.
OR
When using OR as a connector, it specifies that at least one of the keywords you searched must be present in your search results. Unlike AND, using OR will only guarantee that one of your terms is present in the results, not necessarily all of them. When you combine keywords with OR, you’ll retrieve more results than if you searched just one of those terms. This is useful when you want to search synonyms or closely related concepts for your topic simultaneously. The blue shaded area represents dogs OR canines:
Returning to our example, if you want to find more sources about dogs and evolution, using OR allows you to add related terms like “canine” to your search. Here is an example of a Boolean search you can try. The blue shaded area represents:
(dogs OR canines) AND evolution
In the example above, notice how (dogs OR canines) is written in parenthesis. This tells the database to process this part of the search first. It tells the database to first find all the articles that mention either dogs or canines, and then check which of those also have the word evolution.
NOT
NOT will restrict your search by omitting any keyword(s) that come after NOT. This is a useful way to prevent items containing irrelevant or unwanted keywords from appearing in your search results. The blue shaded area represents canines NOT teeth:
Boolean Operators in Different Databases
Some interfaces use Booleans differently:
- Google places an invisible AND between each of your search terms and will attempt to find results with all of your terms before anything else.
- Google uses a minus symbol (-) in place of NOT for Boolean searches.
- JSTOR places an invisible OR between each of your search terms unless you use another Boolean operator between search terms.
- Some databases will suggest a string of synonyms connected with OR after you type a keyword or phrase.
- Some databases will treat everything in the search box as one phrase that has to occur in that order unless you use Boolean operators between keywords.
Challenge!
1. Which Boolean operator will give you the most search results?
a. OR
b. AND
c. NOT
2. Which of these searches would get fewer results?
a. (apples OR bananas) AND peanut butter
b. apples AND bananas AND peanut buter
3. Which search best represents the key concepts of the research question: What effects does Daylight Savings Time have on health?
a. Daylight Savings Time OR health
b. Daylight Savings Time AND health
c. Daylight Savings Time AND health AND sleep