  There are several relations which may fall short of genuine identity, but
which behave like identity in important respects. Such grades of discrimination
have recently been the subject of much philosophical and technical discussion.
This paper aims to complete their technical investigation. Grades of
indiscernibility are defined in terms of satisfaction of certain first-order
formulas. Grades of symmetry are defined in terms of symmetries on a structure.
Both of these families of grades of discrimination have been studied in some
detail. However, this paper also introduces grades of relativity, defined in
terms of relativeness correspondences. This paper explores the relationships
between all the grades of discrimination, exhaustively answering several
natural questions that have so far received only partial answers. It also
establishes which grades can be captured in terms of satisfaction of
object-language formulas, and draws connections with definability theory.
