Co to jest kryterium identyczności?

The article contains the reporting definition for the criterion of identity, a classification of criteria of identity and the general conditions that criteria of identity should meet. The author suggests replacing the binary division of criteria of identity into one- and two-level ones with a ternary division into one level, mixed and two-level criteria. In this suggestion the key role is played by the definition of the range of relation. The article is concluded with a partial solution to the dispute between T. Williamson and E. Lowe over the value of one-level criteria of identity.