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:
ie in believe, fierce, collie, die, friend
ei after c in deceive, ceiling, receipt
The rule is very well known; Edward Carney calls it "this supreme, and for many people solitary, spelling rule".[1] However, its short form as above has many common exceptions; for example:
ie after c: species, science, sufficient
ei not preceded by c: seize, weird, vein, foreign, eider, their, feisty
http://en.wikipedia.org/wiki/I_before_E_except_after_C