Of Mice and Plurals

So slightly off topic:

A couple of weeks ago in the comments of my questions post Sarah asked why, in English, we use 'mice' as the plural of 'mouse', but 'houses' as the plural. Today I finally got around to asking my lecturer about it, like I said I would.

Firstly, the reason we say mouse in the first place. It's a remnant of an ancient plural form where '-iz' would be added to the end of words, and then a process called vowel harmony would make the vowel in the word sound like the i. So mouse (or its precursor, probably something close to the German 'maus') would become mouse-iz, which gets harmonised to mice-iz.

Now, languages hate redundancy, so when you can already tell the plural form from singular, with or without the -iz, the -iz will slowly get dropped from the word, leaving us with mouse/mice.

As for why this doesn't work for house? Well, as my lecturer said, the clue is in the Scottish pronunciation, of HOOOOOOOOS. See, back in about the 1400s, the English spelling system pretty much matched the way we said it, but over the course of a hundred and fifty odd years all the vowels moved around to... well, basically wherever they liked. So mouse, coming from something like 'maus', has always been that 'au' sound, and thus had developed the harmony from the -iz ending. Whereas house, having shifted from the totally different sounding 'hoos', never developed that, even though after the vowel shift it did develop the same sound as mouse.

Interestingly, the German word for house ('haus') has also been vowel shifted from this earlier 'hoooooooos' form, although early enough in the languages history that it now matches the rest of the 'au' type words.

And now you know.