Columbia subject headings:
Harvard subject headings:
Hoffding, Harald, 1843-1931--Correspondence.
Philosophers--Denmark--Correspondence.
Sociologists--Germany--Correspondence.
Tönnies, Ferdinand, 1855-1936--Correspondence.
Princeton subject headings:
Høffding, Harald, 1843-1931--Correspondence.
Sociologists--Denmark--Correspondence.
Sociologists--Germany--Correspondence.
Tönnies, Ferdinand, 1855-1936--Correspondence.