Less, Fewer, and Ancient Marital Disputes

I was at dinner with my father.

I brought up a lovely new word game that Penelope and I had begun playing. The title of the game is "25 words or less". My dear father corrected me and said "25 words or fewer". I said yes yes yes, I know all about that, but let me tell you about this great game.

Instead of listening to me tell him about this game, he launched into a (roundabout) explanation of the difference between less and fewer. I said I know! Less is for mass nouns and fewer is for count nouns. Except, I went on to say, for the case of ONE. You should say one LESS aeroplane, not one FEWER aeroplane.

my father rolled his eyes and said, yeah yeah, that's Martha's favorite thing, but honestly...

All this time I was telling people about the less/fewer exception and it turns out it was nothing but a MOMISM!

I found zero references on the web to anything that corroborates this cockamaime (and its own dubious etymology) theory.

Here's the "Grammar Goddess" on the subject.

This guy thinks the only exceptions are with units of time and money, e.g. I have 500 dollars less than you do, not I have 500 dollars fewer than you do.

Kenneth G. Wilson sums it all up in a pretty tidy paragraph, all without a mention of this "last unit" theory.

I should say that at dinner, I lied and said that I had read this rule in the Chicago Manual of Style of all places, which was an outright lie! And now I find out that it's true, I've been spouting momisms for years!

This is your big chance at vindication. Mother, you always say that your golden rule for grammar is that if smart people say it, it's probably ok to say it too. So find me one other person, smart or otherwise, on this vast internet that thinks like you do, and I'll drop my indignation.