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Boolean searching is based on an algebraic system of logic formulated by George Boole, a 19th century English mathematician.

In a Boolean search, keywords are combined by the operators AND, OR and NOT to narrow or broaden the search (you do not have to enter them in capitals).

AND

The operator AND narrows the search by instructing the search engine to search for all the records containing the first keyword, then for all the records containing the second keyword, and show only those records that contain both.

OR

The operator OR broadens the search to include records containing either keyword, or both.

The OR search is particularly useful when there are several common synonyms for a concept, or variant spellings of a word.  However, if you use the OR search in combination with other searches, you must enclose it in parentheses (see below).

Examples:

• adolescent or teen?
• medieval or "middle ages"
• vergil or virgil

It is also useful if you have a complex search that you wish to run with several options (for example, for various geographical areas), and you wish to run it once rather than repeat it.

Example:

puritan? AND women AND (massachusetts OR connecticut OR "rhode island" OR "new hampshire")?

NOT

Combining search terms with the NOT operator narrows the search by excluding unwanted terms.

These Venn diagrams help to visualize the meaning of AND, OR and NOT; the colored area indicates the items that will be retrieved in each case.

In the Keyword Boolean search, you also have the option to use a field code to search a specific field in the CLIO catalog record.  To restrict the search to a specific field, enter the appropriate code for the field (see list below), followed by a space, and then your search terms.

Example:
nkey shakespeare and tkey hamlet finds records with Shakespeare in the author field and Hamlet in the title field

For more field codes, see the Field Codes for Keyword Searching page.