Scholarly books can also be excellent sources for establishing historical and cultural background or placing your topic in context with related issues. A scholarly monograph:
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Collins Library uses Library of Congress Subject Headings to describe the content of books. In many ways, subject headings are a form of tagging, in that they represent the content of the material and provide ways for you to efficiently locate more materials that are conceptually related.
Broad focus (examples):
France -- Civilization -- 17th century
France -- History -- Revolution, 1789-1799
France -- Intellectual life -- 18th century
Paris (France) -- Social life and customs -- 18th century
Middle class -- France -- History
Specific focus (examples):
Clothing trade -- France -- History
Fashion -- France -- History -- 17th century
Textile design -- France -- History -- 18th century -- Catalogs