I am cited in John S. Wilkins and Malte C. Ebach’s thoughtful book The Nature of Classification. Relationships and Kinds in the Natural Sciences, 2014.I am grateful to John Wilkins, colleague and friend, for the fascinating conversations we had; to both authors for mentioning my name; and to Alessandro Minelli for pointing out this reference to me.
The authors write on p. 95:
Broadly speaking, taxonomic identity is intersubstitutability […]. But in biology and in the special sciences generally, identity is never total, so discernibility relies on what information we have and what degree of resolution or fine-grain we are dividing the domain into. Emanuele Serrelli suggested in conversation that identity relations in a domain are in effect insensitivity to the properties to be used to classify. Choosing some different criteria to evaluate should give you the same answer – X is a member of the kind A whether you use criteria p or criteria q. However similarity relations depend exactly on the criteria or properties used. Complete similarity relies on an absence of variability. Identity relations do not.