Nobody on my teachers mailing list (even the native speakers) can give an explanation about the difference in spellings of four/fourteen/forty. The initial post was from a teacher who couldn't answer one of her pupils.
I suggested that spelling was not so compelling at a time, and that it was probably spelled many different ways, but usage just kept the current ones. I added that for "four", maybe it was to avoid confusion with "for", whereas for "forty", there was no problem.
Someone replied "what about fourteen?".
- no other word can be confused with "fourteen" or "forty", so the problem was only with "four". The random spelling with the others didn't matter much;
- or maybe it has something to do with the way these words were sounded in the past: ou/o before long/short vowel sound.
This is of course pure hypothesis, and I'd really like to know if anyone can tell me if they have sound information on that detail...
maybe it has something to do with the way these words were sounded in the past: ou/o before long/short vowel sound.
Well, here's what I remember from a historical linguistics course I took 4,000 years ago.
"five" ([ai]) was reduced to fi- ([I]), when -ty (<-tig) was added, giving 'fifty', see also 'fifteen'; "three" was reduced to thr-, when -ty was added, giving 'thirty', see also 'thirteen', and so "four" followed the same pattern: "four" (OE. feo'wer / feour-) reduced to feor-, giving modern day 'fo:rty'.
"five" and "three" have one syllable each, whereas OE. feower ("four") had two syllables. (note, there are speakers today, though, who pronounce "four" as [fo:'wr], with two syllables, but never *fo:'[w]rty, unless emphatic.)
Add a suffix, either -ty or -teen, and the stress along with its associated vowel changes. (note, -ty and -teen share the same vowel, but differ in vowel length and stress.) In the case of feo'wer+tig ("forty") the second syllable was reduced, and in the case of feo'wer'teen ("fourteen") the first syllable was reduced.