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 digraph ⟨ei⟩ or ⟨ie⟩, the rhyme suggests that the correct order is ⟨ie⟩ unless the preceding letter is ⟨c⟩, in which case it may be ⟨ei⟩.

The rhyme is very well known; Edward Carney calls it "this supreme, and for many people solitary, spelling rule". However, the short form quoted above has many common exceptions; for example:

⟨ie⟩ after ⟨c⟩: species, science, sufficient, society

⟨ei⟩ not preceded by ⟨c⟩: seize, vein, weird, heist, their, feisty, foreign, protein, weigh, neighbor

However, some of the words listed above do not contain the ⟨ie⟩ or ⟨ei⟩ digraph, but the letters ⟨i⟩ (or digraph ⟨ci⟩) and ⟨e⟩ pronounced separately. The rule is sometimes taught as being restricted based on the sound represented by the spelling. Two common restrictions are:

excluding cases where the spelling represents the "long a" sound (the lexical sets of FACE and perhaps SQUARE ). This is commonly expressed by continuing the rhyme "or when sounding like A, as in neighbor or weigh".

including only cases where the spelling represents the "long e" sound (the lexical sets of FLEECE and perhaps NEAR and happY ).

Variant pronunciations of some words (such as heinous and neither) complicate application of sound-based restrictions, which do not eliminate all exceptions. Many authorities deprecate the rule as having too many exceptions to be worth learning.