Columbia subject headings:
Middle class--Portugal--History--18th century.
Middle class--Portugal--History--19th century.
Portugal--Commerce--History--18th century.
Portugal--Commerce--History--19th century.
Harvard subject headings:
Middle class--Portugal--History--18th century.
Middle class--Portugal--History--19th century.
Portugal--Commerce--History--18th century.
Portugal--Commerce--History--19th century.
Princeton subject headings:
Middle class--Portugal--History--18th century.
Middle class--Portugal--History--19th century.
Portugal--Commerce--History--18th century.
Portugal--Commerce--History--19th century.