It's complicated
"
Describes quantifiable things" gets at the problem. Bullshit is a descriptor. It can straight-up be an adjective – you can call something bullshit – but even when bullshit is a noun, it exists to both communicate a noun
and an adjective. You can pretend the noun
bullshit is short for "bullshit claim," where
bullshit is the adjective again, and
claim is the noun. The "claim" noun is unsaid in the phrase
bullshit (noun), but it's implied, and that implication helps us be less wordy.
Therefore, bullshit does not mean "a group of multiple lies," or more generally "a group of quantifiable things" in the same way that a
flock of multiple birds does. And indeed
flocks works as a plural. Remembering bullshit's adjectival role, the lack of a plural makes more sense. You wouldn't say "beautifuls" to describe multiple things that are beautiful – conventionally anyway, don't let me stop you, I'm a descriptivist – you'd say "beautiful things." For
bullshit (noun), it's the same principle, but we just undo the phrase shortening and unpack
bullshit into its full and explicit form, "bullshit thing." Then we add the plural onto
thing, like with beautiful.
So we have a reason why bullshit lacks a conventional plural. But could that reason itself still be arbitrary? Well... probably still, yeah. We're drifting closer to
language nerdery, when my domain is the similar but not-quite-identical
communication nerdery, so I would not say I have all the answers. English handles "adjectivey nouns" in a lot of different ways, and I'm just not completely aware how much of those differences are "for reasons" versus "for reasons, with exceptions" versus "for delicate fine-grained reasons that are subtle enough to often function as vibes in practice" versus "for vibes, straight up."
I started mucking around for a more detailed answer and found the muck-to-insight ratio was not great, so I'll leave it at this.
Plurals of adjective-nouns vary widely in acceptedness and usage.
Some adjective-nouns straight up have plurals. Reds is definitely a word. But it's generally constrained to specific situations – specific shades of color come to mind, as do red wines, and a proper noun for a baseball team. Using
reds more generally, like to describe multiple miscellaneous red objects, would get you a similar type of confusion to
bullshits.
Some adjective-nouns have slightly modified noun forms, like accura
te versus accura
cy. These nouns may have straightforward plurals, like "accuracies", which often fit into a mold of "not seen as
wrong, but awkward in practice, in part because of limited use cases." Beautiful becomes beauty as a noun, and "beauties" is definitely a word, but specifically for a group of people, not other contexts, and can come across as demeaning if used carelessly.
Sometimes these plural nouns are more straight up not used. Literate becomes literacy, but people don't say literacies, they say literacy rates.
Some have more intense modification. Peanut butter and jelly is a compound adjective that usually only makes sense in the context of the noun peanut butter and jelly sandwich, which is often modified in practice to the PB&J abbreviation, and PB&Js works as a plural form, but again the use cases are a bit niche.
I love word nerdery
