what words break the i before e rule
I before E except after C "I before E, except after C" is a mnemonic rule of thumb for English spelling. If one is unsure whether a word is spelled with the sequence ei or ie, the rhyme suggests that the correct order is ie unless the preceding letter is c, in which case it is ei. For example:
Great Vowel Shift After around 1300, the long vowels of Middle English began changing in pronunciation. The two close vowels, /iː uː/, became diphthongs (vowel breaking), and the other five, /eː ɛː aː ɔː oː/, underwent an increase in tongue height (raising).