Boolean Operators: 
What May Happen when You Don't Use Them

You may find satisfactory search results without Boolean Operators. It depends on the database. Some databases may add certain default Boolean Operators to your search terms. For example, Google automatically adds Boolean AND between every search term you enter. If you're having difficulty finding sources without them, the information below may be why.

When you enter search terms without using a connector, such as the following search:

be aware that the database may be set up to do one of three things with your search terms:

1. ozone AND layer AND depletion
   Most databases assume the Boolean term AND between words in a phrase and will search for records containing all three terms but not necessarily next to each other in that order. Your results will include all three words, but ozone could appear on page 1, layer on page 4, and the depletion on page 6 of an article.
2. ozone OR layer OR depletion
   Other databases may assume the Boolean term OR between words and will search for items containing any of the terms. This will retrieve thousands of irrelevant records, with some containing just the word ozone, for example, and others just the word depletion.
3. ozone layer depletion
   Or a database may assume a phrase, requiring that the words be right next to each other. A phrase search looks for words that are adjacent to each other in the exact order they are typed by you. In this case, your results will include articles with ozone layer depletion just as it is written. You'll learn more about phrase searching on the next page.

As you can see in the examples above and on the previous pages, the use of AND or OR as a connector can have a significant effect on the results of your search. If you are unsure how a database will interpret your search, consult the database's search tips or  pages.

Below is example of the SIRS database search tips for using Boolean operators.