Here's one sentence from "The grammar book. An ESL/EFL teachers course by Celce-Murcia and Larcen Freeman.
In some preliminary research Bergsnev(1976) has shown that abstract nouns derived from verbs and adjectives often have both a mass and a count form for expressing a generality in English,e.g:…
The bold part of phrase is what sort of puzzles me. Coordination is a vast subject consisting of numerous different points and nuances that pretty often may result in ambiguity and vagueness.
Both a mass and a count form - at first sight seems to be okay. As may be noticed, this is just ellipsis of the word "form".
But, shouldn't it be "a mass and a count forms - then?
That has never given rise to difficulties for me, but now having started analyzing the sentence and trying to look up "coordination" in "A comprehensive grammar of the English language I'm being rather doubtful.
So the question is - what is the rule of coordination that's being used in this example and why not use the plural form of the noun?