Another great example of a rule that exists in English that native speakers generally follow without knowing, but is taught to learners of English as a second language, is the rule of which adjectives form comparatives and superlatives by suffixing '-er' and '-est', and which by prefixing 'more' and 'most'.
As a native English speaker I was never taught a rule that explains why I would say hotter or wrigglier or redder or wildest or shiniest, but more emphatic, more open, most excellent or most orange. I'd always assumed adjective -er and -est suffixes were just irregular, with no pattern to them at all.
But it turns out there's basically a simple rule - if it ends in '-y' or has only one syllable, you suffix it; otherwise you use the 'more' or 'most' form. It's remarkably solid as a rule, and even when I come up with a word that sounds sort of right to my ear that doesn't follow the rule - like, for example, I can kind of see 'wickedest' as being a valid form - it turns out that if I think about it, it probably doesn't sound right after all, and I would probably prefer 'most wicked'.
It's good practice to check your intuition on things like this against a searchable corpus. According to http://corpus.byu.edu/coca/, "most wicked" just barely edges out "wickedest" in terms of frequency, 22 to 20.
It's a practice, but as an English speaker I have the privilege of making my own corpus up as I go along. When I say I find I prefer 'most wicked' to 'wickedest', I'm expressing the subjective opinion that I think I would fall in the 22 part of that corpus, not the 20 - if anything I wrote about relative wickedness were to make it into the COCA corpus that number would go up to 23.
But that would be true even if I were in the minority. The corpus is just going to reflect usage, and my usage is as valid as any other, so... while it provides some sort of peer validation, it doesn't answer the question of whether one form or another is 'more correct', only whether one is 'more common'. Or commoner, maybe. No, I'm going to stick with more common.
As a non-native English speaker, I find this to be a precious suggestion. I'm going to try and use it for those situations of uncertainty between two forms. I usually resort to some specific google search, but that's often ineffective, especially if the "wrong version" is pretty common among a subset of international speakers.
"Simple," "narrow," "clever," and "quiet" are usually listed as exceptions to the rule, and their suffixed superlative forms also usually appear in dictionaries.
Good point. A google search also shows that since "fun" has only recently migrated from a noun to an adjective, the -er/est forms are not yet accepted, but will likely become standard over time.
Have you considered that it may have something to do with the adjectiveness or adverbiality of the word? Words that are exclusively single-use readily take the -er and -est suffixes, whereas those that perform double or triple duty as nouns and/or verbs as well (perhaps as inflected forms) are less apt to sound correct when suffixed.
Since -ly is an adverbizing suffix, most anything ending in -ly could also end in -lier or -liest. A dual-purpose word might generate ambiguity when using -er, because -er is also used to transform a noun or verb into an associated noun, much like -ing changes a verb.
"Opener" could be an adjective meaning less enclosed, or it could be a person or device that opens things.
Hot may become hotter and hottest, but heated can only become more heated, because it is already heat and -ed, and the suffixes won't combine. Old becomes older and oldest, but aged only becomes more aged. Red -> redder -> reddest; rouged -> more rouged.
Likewise, the -tic suffix does not combine. Emphatic is already an adjective form of emphasis. The -er and -est suffixes tend to attach more easily to a word that was originally a modifier rather than a noun or verb, because only a few suffixes that modify part of speech combine. I wonder if it would be better to be "most emphatic" or "most emphasized"?
The rules are complicated because English grabs vocabulary from so many other languages, and the words with germanic, romance, greek, or other etymologies don't always play well by the same rules.
Native English speakers are somehow able to apply etymologically consistent alteration rules to words based on the qualities of their sound rather than by their actual source language. That's how we got "cherry". The French word was "cerise", which was imported as "cherries". Obviously, by English grammar, a word ending in the /s/ or /z/ sound is a plural. So you chop off the /z/ to get the singular "cherry". English has sort of a Procrustean Bed approach to word acquisition. If it don't fit, we makes it fit.
I'd considered it when I had assumed it was a somewhat irregular pattern, but as I say, it turns out there is a rule and that isn't it.
You're right that '-ed' suffixes prevent '-er'/'-est' being appended even if they don't add a second syllable to their root, though in most cases '-ed' makes a word multisyllabic so forces it down the 'most' route. 'bored' or, as you say, 'rouged' are monosyllabic exceptions, though. And that's in spite of there being no awkward sound created - you could certainly say 'boreder' (it's pronounced just like 'border' or 'boarder'), but it's not a word. English is weird.
But with 'open', I don't see your point. It's interesting, in fact, that even though the word 'opener' is a valid word, in the context of a 'can opener', say, it is not a valid comparative for open. It is wrong to say 'The light through the large window makes this room much opener than that one' - you should say it makes it 'much more open' instead. But you could say it made it 'much brighter'.
Opener was an example of a potentially ambiguous word. That may be why the superlative -er is not allowed. The noun-forming -er prevails over the adjective-forming -er.
Nope, open takes 'more' because it's bisyllabic, not because it avoids a collision with the noun 'opener'. Lighter, warmer, cooler... all common enough verb-based nouns that collide with comparatives and don't take 'more' because they're monosyllables.
Your simpler explanation is certainly cleverer than mine, by far. My narrower criterion obviously has several counterexamples, so I should probably be quieter about it until I can gather more supporting evidence.
English is complicated. Let's not pretend that we know about some intentionally engineered structure in it when we're really just noticing patterns and correlations.
I distinctly remember being taught the one syllable rule in elementary school in the US. There are, of course, some exceptions, like "narrower" and "quietest," and "stupidest."
To me, "most stupid" sounds hipster or foreign, while stupidest just sounds right - in normal speech. "He is the most stupid" is perhaps more memorable for sounding off: It's natural to emphasize "most".
Is he more stupid or stupider? I would say stupid, stupider, stupidest, red, redder or more red, reddest, and brilliant, more brilliant, most brilliant, but smart, smarter, smartest.
As a native English speaker I was never taught a rule that explains why I would say hotter or wrigglier or redder or wildest or shiniest, but more emphatic, more open, most excellent or most orange. I'd always assumed adjective -er and -est suffixes were just irregular, with no pattern to them at all.
But it turns out there's basically a simple rule - if it ends in '-y' or has only one syllable, you suffix it; otherwise you use the 'more' or 'most' form. It's remarkably solid as a rule, and even when I come up with a word that sounds sort of right to my ear that doesn't follow the rule - like, for example, I can kind of see 'wickedest' as being a valid form - it turns out that if I think about it, it probably doesn't sound right after all, and I would probably prefer 'most wicked'.