Subject headings are specific vocabulary that the Library of Congress assigns to published material. You can search the Catalog for books and other materials related to historical research by subject heading. General subject headings in history follow a specific pattern: Place name -- Subject -- Subdivision -- Time period.
Place names:
Can be names of countries, regions, states, or cities.
Subject
Describes the particular emphasis of the item.
Subdivisions:
Describe the a narrower emphasis of the item.
Time period:
Refers to the years covered by the item. Time period designations vary according to place name as well as to subject and subdivision, and are not included for all headings.
The following examples illustrate possible subject searches for migration to and from Pennsylvania:
| Place Name as Subject | Subject | Subdivision | Time Period |
|---|---|---|---|
| Pennsylvania | Emigration and Immigration | ||
| Pennsylvania | Emigration and Immigration | Early works to 1800 | |
| Pennsylvania | Emigration and Immigration | Germans | |
| Pennsylvania | Emigration and Immigration | History | |
| Pennsylvania | Emigration and Immigration | History | 18th century |
| Pennsylvania | Emigration and Immigration | History | 19th century |
| Pennsylvania | Emigration and Immigration | Periodicals |
Sometimes, however, you may find an alternate pattern, with a specific subject listed first, then a palace, either a subject or geographic subdivision or a time period, another subject, and a date range. For example I have pasted in the first entries for anarchism in Spain:
| Subject | Place | Subdivision/Time Period | Subdivision | Time Period | Subdivision |
|---|---|---|---|---|---|
| Anarchism | Spain | ||||
| Anarchism | Spain | 19th century | |||
| Anarchism | Spain | 20th century | |||
| Anarchism | Spain | Almería (Province) | History | ||
| Anarchism | Spain | Andalusia | History | ||
| Anarchism | Spain | Andalusia | History | 19th century | |
| Anarchism | Spain | Andalusia | History | 20th century | |
| Anarchism | Spain | Andalusia | Periodicals | ||
| Anarchism | Spain | Aragon | |||
| Anarchism | Spain | Aragon | History | ||
| Anarchism | Spain | Asturias | |||
| Anarchism | Spain | Barcelona | |||
| Anarchism | Spain | Barcelona | History | ||
| Anarchism | Spain | Barcelona | History | 19th century | |
| Anarchism | Spain | Barcelona | History | 20th century | |
| Anarchism | Spain | Barcelona | History | 20th century | Fiction |
| Anarchism | Spain | Barcelona (Province) | History | 20th century | Congresses |
| Anarchism | Spain | Benalup de Sidonia | History | ||
| Anarchism | Spain | Benalup de Sidonia | History | 20th century |
Notice the last two entries are for the pueblo in Andalusia better known as Casas Viejas. The Library of Congress subject headings do not give you complete geographical information and they persist in using the current official name for geographic locations. Bear this in mind when you look for events (Siege of Leningrad is now "Saint Petersburg (Russia) -- History -- Siege, 1941-1944"), or counties that no longer exist (East or West Germany are plain Germany).
For more information, consult the Library of Congress Authorities online (see below) or the five printed volumes in Reference, Library of Congress Subject Headings (LCSH), which contains the subject headings used in the NYU Libraries' Catalog and other library catalogs. Look under the place name or subject to see the appropriate subdivisions and time periods.