All known religious beliefs, whether simple or complex, present one common characteristic: they presuppose a classification of all things, real and ideal, of which men think, into two classes or opposed groups, generally designated†profane and sacred.

-Durkheim, EŁ  mile
  The Elementary Forms of the Religious Life (translated by Joseph Ward Swain,1965).

It is always easy to find fault with a classification. There are a hundred ways of arranging any set of objects, and something mayalmost always be said against the best, and in favour of the worst of them. But the merits of a classification depend on the purposes to which it is instrumental.

-Mill,John Stuart
  Auguste Comte and Positivism.