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Finding Theses and Dissertations

Combining Terms with AND, OR, and NOT

When you get too few or too many (and too irrelevant) search results, one way to improve results is to use the simple words AND, OR, and NOT. The way these familiar words are used in databases and catalogs--where we call them Boolean Operators--can take some getting used to.

Combining Terms

There are several ways to combine terms, each with very different results.

First, it helps to know that most databases do not search the full text of articles. They search the information about the articles: the article title, the journal title, the author, the abstract (summary),  etc. 

Suppose you type these words in a search box:

internet privacy

What happens? It depends on the search tool. Some will treat it like a phrase, as if it has quotation marks around it. Others may insert "AND" between the two words. A few even insert "OR." Some (like Google) treat it as all of the above, and rank results with the whole phrase higher than results where the two words are separated.

If you want to force a search tool to treat it like a whole phrase, put quotation marks around it:

"internet privacy"

Boolean operator: AND

When you use AND and two keywords, the interface will return a list of every record that contains BOTH the first term AND the second term. This kind of search will always reduce the number of records.

If you combine too many terms with AND, you may return no records at all, because some terms might not overlap.

This is the most common way to combine terms.

Boolean operator: OR

When you use OR and two keywords, the interface will return a list of every record that contains either the first term OR the second term. This kind of search will always increase the number of records.

If you combine too many terms (or a few terms that are too broad) with OR, you will return an unmanageable number of records.

OR is usually used when there are multiple synonyms, and you don't want to accidentally limit your search. For example:

students OR pupils

Boolean operator: NOT

Venn diagram showing search for internet AND Privacy NOT security

When you use NOT, the database will return a list of every record that contains the first term, but exclude any record with the term after NOT. This kind of search will always reduce the number of records.
NOT is usually used in conjunction with an AND search, to exclude records that are unrelated to your goals but cluttering the search results:

internet AND privacy NOT security.  

Google tip: did you know you could use a minus sign in Google to mean "NOT"? Try these two searches in Google to see what happens:

Benedict

Benedict -Cumberbatch

Other Search Hints

Asterisk *

If your search involves words like "children" or "pupils", you don't want to accidentally rule out records with words like "child" or "pupil". To save you the trouble of using OR in these cases, most databases let you use an asterisk in place of a word ending:

child* OR pupil*

This search will return results with child, children, pupil, or pupils. (Be careful, though; it could also return "childcare.") Some databases now automatically return results with different endings, or even return results with endings removed, which means you might not need to use the asterisk. If your search results contain different forms of your keyword (e.g. singular and plural), then the database adds the asterisk for you.

Google Advanced Search

Yes! Google has a secret Advanced Search. It's not really secret; it's just not obvious. Look under the gear icon google gear icon on the search results page.

Parentheses ( )

In most databases, you can construct more complex searches by using parentheses or by using multi-line searches. (Each separate line is treated like a set of parentheses.) If you want to search internet AND privacy, but want to add some synonyms to the search and don't want results about security:

(internet OR web) AND (privacy OR rights) NOT security

Proximity Searching

Some databases allow you to search based on how close two terms are to each other. You might only want articles with two terms within a few words of each other. The exact phrasing may differ depending on the database company (tip: check the Help page), but a proximity search for two terms within 5 words of each other might look like this:

baseball N5 players

This would be a slightly broader search than the phrase "baseball players" in quotes.

Search in:

Title, Author, Subject, Journal Title, etc.

Most databases let you choose which fields to search. The default is usually "any field," which searches all of the information about an article. This can be quite useful if you want to combine, say, a subject term on one line with a keyword on another line. It can also be handy if you have the bibliographic information, and just want one article: just select Author in the first line and Title in the second. (Usually, an author's last name and one distinctive word or phrase from the title will be enough to limit your search to one the article you want.)