Here are examples of a search by keyword and a search by subject. Look at the differences in the kind of information you get as a result of each search.

When you begin research on a topic, you generally don't know any important titles or authors in the field, so you would begin by searching for the subject of your research and not for an author or title. In library search tools you can search this way by Keyword or by Subject.

In searching a library resource you can have the search engine look at the whole record for your terms or it can look in specific fields. A Keyword search will look for your terms in all of the basic fields of each catalog record. It's a broad search that will retrieve records that include your "key words" in almost every part of the record. It is so broad that it will probably bring up many irrelevant records. Keyword searching is useful for "mining" more precise terms to help focus the research.

Example:
Keyword search "education and encyclopedia" will certainly bring up records for the encyclopedias about education that the library holds.

In a subject search, the catalog's search engine looks for your terms only in the Subject field. The catch is that the catalog uses a controlled vocabulary - Library of Congress Subject Headings - and your terms have to match LCSH to be effective. Using the right terms will bring highly relevant and focused results.

Example: Trying a Subject search for 'american civil war' will not retrieve any records because this is not a LCSH. The catalog may refer you to the correct LCSH, 'United States History Civil War, 1861-1865.'