In item 21 of my ideas for spelling reform post I mused about whether the FOOT vowel should be spelled with short U or with OO in reformed spelling. In the first proof of concept, I chose short U. There was only one word with this vowel sound in that text, though (should -> shud).
Whichever option we choose, the set of words with FOOT is a small set, and because of this it carries a low functional load.
Since the set is small, I thought, why not list all the words in it, and look for possible collisions that might happen in reading depending on the choice we make on how to spell them. So far this is the list I have come up with:
Put, full, pull, bull, bush, push, tush, pudding, sugar, butch, whup, puss, kush, cushion, foot, good, wood – would, look, book, hood, cook, toots, crook, soot, booger, wool, brook, nook, hook, shook, took, woof, whoops, could, should, woman and wolf belong to this set. Room, broom and cuckoo belong to this set for some speakers, and to the GOOSE set for other speakers, including me. Mush belongs with STRUT for some speakers (like me) and with FOOT for others.
Let’s start with the possible collisions if we spell FOOT with the GOOSE set as OO. Since this reform would leave proper names alone, we don’t need to worry about look / Luke. If we spelled FOOT with OO, full, pull, cook, puss and would would be spelled like fool, pool, kook, poos, wood, which is also how you spell those words in traditional spelling. Would – wood presents no trouble since they are homophonous to begin with, and this new spelling does not seek to spell words that sound the same differently, but the other four word pairs do not sound the same (provided you contrast FOOT and GOOSE in your accent, which many people in Scotland and Ulster do not).
There would also be some collisions with new spellings of some words. Wood – would, hood, soot, could, should would be spelled just like the new spellings of wooed, who’d, suit, cooed, shooed (-> wood, hood, soot, kood, shood). Nook would also collide with the new spelling of nuke, unless we chose instead to spell this last word nuuk on account of its variant pronunciation with CUTE instead of GOOSE.
If we spell FOOT with STRUT, that is, with short U, booger would be spelled bugger and puss, pus. People who pronounce room like FOOT might spell it rum, which would collide with the spirit. As for collisions with new spellings, put, look, book, cook, could, hook, shook, took would in their new spelling collide with the new spellings of putt, luck, buck, cuck, cud, huck, shuck, tuck (-> put, luk, buk, kuk, kud, huk, shuk, tuk). This would not be a problem for people who do not contrast STRUT and FOOT in their accent, like many speakers in the north of England and some in Ireland. But it would be a problem for everyone else.
I am bound to have forgotten a few words with the FOOT vowel. Do mention it in the comments if you think of any others.