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Understanding Boolean Logic in Search Engines

Written by Eileen Parzek, © 2003

Most people who are online have a general sense of what a search engine is, a favorite or two, and method of searching which may or may not garner them results. Many times, search engines are frustrating because although WE know what we want, knowing how to speak Google (the number one search engine as of this writing) isn't always clear. What people are not often familiar with is the idea of "Boolean logic" - a technical term which describes the way that databases are searched for optimal search results. Although search engines tend to be non standardized in how they allow and optimize searches, there are some concepts which, once understood, should help you use these powerful tools to harness the information that is online.

Boolean logic consists of three operators: AND, OR, and NOT. In other words, when you are searching, you need to tell the search engine precisely what you want returned. Google makes it simple by automatically assuming the AND operator is in place, and returning only the pages containing both words. The search for

Cat Allergies

would return web pages with both cat AND allergies on it.

But maybe you aren't sure which word to search for - and want to get the best results. So you might use

Cat OR Feline

in Google, in order to get both words on the page.

In some search engines, you can require a word to be found in the results. For example, in Google, the following search:

Cat OR Feline +allergies

would result in web pages about cat or feline allergies!

You can also group phrases which need to be exact. Although the previous search will get you every page with cat OR feline and allergies on it, you might want to specify the phrase cat allergies. To do that, you can use quotes, like this:

"cat allergies"

Although we've talked about Google, the basic concept of Boolean logic applies to all search engine databases, and most sites have a help page which will specify precisely what structure is used there. Some search interfaces simplify the process by making the choice "All of these words/Must contain the words" available on the web form, but they are still using Boolean logic underneath it all!

Since the chief source of frustration for many people is that they can't find things online, understanding how to search with Boolean operators can really help you harness the information on the web. Give it a try!


Eileen Parzek is an award winning graphic and web designer providing digital and print graphic design and web design services. Always found at the intersection of information, creativity and technology, her business, Business Design Studio (www.businessdesignstudio.com) helps small businesses make a big impression.

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