Many languages mark a grammatical distinction that is commonly referred to as the "mass/count-distinction"; for example, the distinction between the occurrences of "hair" as a mass-noun in "There is hair in my soup," on the one hand, and its occurrences as a singular and plural count-noun in "There is a hair in my soup" or "There are hairs in my soup," on the other. Awareness of this linguistic contrast may, in the Western tradition, date as far back as the pre-Socratics, Plato, and Aristotle; in modern times, however, the first explicit formulation of it is usually credited to Otto Jespersen (1924).

1. the Problem of Classification

Almost every aspect of the mass/count-distinction is unclear and contested, including the question of how it is to be drawn:

The Problem of Classification:

(i) Between what sorts of entities is the mass/count-distinction to be...