How well does the spelling rule “i before e except after c” hold? I searched the 5,000 most common English words (from here) to see.
70% of the words containing ‘ie” or “ei” follow the rule.
If you weigh the word counts by word frequency, the rule only holds 54% of the time.
There’s a longer version of the rule that adds “or when sounding as ‘a’ as in neighbor or weigh.” This version holds for 79% of the words in my list. And when weighted by frequency, the rule holds 85% of the time.
Update: Here’s an even more accurate version from Merriam-Webster:
i before e,
except after c,
or when sounded as a,
as in ‘neighbor’ and ‘weigh’,
or when it appears in comparatives and superlatives like ‘fancier’,
or when the c sounds as sh as in ‘glacier’,
or when the vowel sounds like ee as in ‘seize’,
or i as in ‘height’,
or when it shows up in compound words such as ‘albeit’,
or when it shows up in –ing inflections of verbs that end in e, like queueing,
or occasionally in technical words that have a strong etymological link to their parent languages such as ‘cuneiform’ and ‘caffeine’,
and in numerous other random exceptions such as ‘science’, ‘forfeit’, and ‘weird.’