Columbia subject headings:
Chaadaev, P. I︠A︡. (Petr I︠A︡kovlevich), 1794-1856.
Harvard subject headings:
Chaadaev, P. I︠A︡. (Petr I︠A︡kovlevich), 1794-1856
History--Philosophy
Princeton subject headings:
Philosophy, Russian.
Russia--Intellectual life.