The term Boolean logic is named after George Boole, a 19th century English mathematician who devised algebra logic; Boolean logic uses logical operators (also called Boolean operators) to coordinate the search for information. It is an information retrieval technique effected mainly in computer operations and using the three Boolean operators OR, AND, and NOT.

Search: Italian OR French paintings Result: 50 records

Italian paintings 20 records

French paintings 38 records

Italian and French paintings
8 records

The Boolean operator OR expands the search and retrieves everything within the blue shaded area of the two circles: the 38 records indexed under French paintings and the 20 records indexed under Italian paintings. The search retrieves 50 records, not 58 records, because 8 records are indexed under both schools of paintings (30 records are indexed under French paintings and 12 records are indexed under Italian paintings).

Search: television AND violence Results: 25

Television 100 records

Violence 150 records

Television and violence
25 records

The Boolean operator AND limits the search and retrieves only the records that contains both indexed terms (indicated by the dark shade area in the middle here). In this case, only 25 records with both concepts are retrieved among the 100 records indexed under television and the 150 records indexed under violence.

Search: paintings NOT portraits Result: 160 records

Portraits 180 records

Paintings 200 records

Portrait paintings
40 records

The Boolean operator NOT is the least frequently used of the three operators. It limits the search and it is used when you want to exclude a specific and clearly defined subtopic within a whole subject area. Here, the operator NOT limits the search and retrieves only 160 records (indicated by the green shade area here) among the 200 records indexed under Paintings (of all types). The operator NOT excludes the 40 records indexed under Portrait paintings, hence only 150 records are displayed.