Full Idea
Syntactic criteria for mass nouns include that they admit 'much' and 'a little', and resist 'many' and 'few'.
Gist of Idea
Mass nouns admit 'much' and 'a little', and resist 'many' and 'few'.
Source
Peter Simons (Parts [1987], 4.6)
Book Reference
Simons,Peter: 'Parts: a Study in Ontology' [OUP 1987], p.154
A Reaction
That is, they don't seem to be countable. Sortal terms are those which pick out countables.