I’m not sure i understand the question, big->bigger is not a special case. Are you asking why that particular rule exists?

Are you asking why that particular rule exists?

No, I’m asking what the rule is, but now I’m not sure that you’re an english teacher so it doesn’t matter.

Well, at a guess, single syllable (edit), ending as -vc, then double the last letter.

fat – fatter
hot – hotter
red – redder

seems to fit

fit – fitter

no, not a English teacher, but I was taught by one, so if you need any other help with the language, please just ask.

Thanks. 😀

Of course it’s acceptable but it’s the exception and not the rule, that is to clarify any ambiguity

The code is more what you’d call “guidelines” than actual rules. But abbreviations are OK with an apostrophe, especially if they serve to clarify. so they are OK normally, but even more so when they serve o clarify.

Rule 11

The plurals for capital letters and numbers used as nouns are not formed with apostrophes.

Examples:
She consulted with three M.D.s.
BUT
She went to three M.D.s’ offices.
The apostrophe is needed here to show plural possessive.
She learned her ABCs.
the 1990s not the 1990’s
the ’90s or the mid-’70s not the ’90’s or the mid-’70’s
She learned her times tables for 6s and 7s.

Exception:
Use apostrophes with capital letters and numbers when the meaning would be unclear otherwise.
The point of an exception being that you can’t use the apostrophe with wild abandon then simply using ambiguity and clarification as the justification.
Hence the question of big/bigger, the single vowel and single consonant rule works in single syllable adjectives.
How do we explain slow/slower? Why not slowwer?

At this point I imagine the OP feels like the child of a messy divorce.

Can’t you two just have angry sex?

How do we explain slow/slower? Why not slowwer?

We? well, I’d probably go for the “Doesn’t have a vowel sound” defence

well, I’d probably go for the “The “w” Doesn’t have a vowel consonant sound” defence

There’s a rule and exceptions but you can’t apply the exceptions arbitrarily.
Better shut up now, wannabe mod is waving his imaginary banhammer! 😳

yeah sorry, meant consonant.

I agree, we should stop there and agree that I won.

So there you have it. If you want to demonstrate your interest in large vehicles, spend two pages of your CV debating the finer intricacies of apostrophe usage.

Tell me you haven’t learnt something, because I have.

Yeah, people on here are consonantly arguing.

Tell me you haven’t learnt something, because I have.

I’ve learnt to skim read

And I’m still learning. It’s the post that keeps on giving…