What is "sortal"

Sortal \Sort"al\, a. Pertaining to a sort. [Obs.]
--Locke.

a. (context philosophy English) Of or pertaining to a sort n. (context philosophy English) A type of universal that defines a particular sort of object

Sortal is a concept that has been used by some philosophers in discussing issues of identity, persistence and change. The simplest property of a sortal is that it can be counted, i.e. can take numbers as modifiers. For example, "pea" is a sortal in the sentence "I want two peas", whereas "water" is not a sortal in the sentence "I want water". Countability is not the only criterion. Thus "red thing" in the sentence "There are two red things on the shelf" is not treated as a sortal by some philosophers who use the term. There is disagreement about the exact definition of the term as well as whether it is applied to linguistic things (like predicates or words), abstract entities (like properties), or psychological entities (such as concepts).