I before E except after C

     [This is a fast-access FAQ excerpt.]
This old schoolroom spelling rule is supposed to help remember
the spelling of vowels pronounced /i:/, the long "e" sound of "feed".
It has no value for words where the vowel is pronounced in any other
way, the key fact which people bemused by many "exceptions" to the
rule usually do not realise.  A version often cited in the U.K.
makes the restriction clear:
    When the sound is /i:/,
    it's I before E
    except after C.
A common U.S. version:
    ...
    or when pronounced /eI/
    as in "neighbour" and "weigh".
is misleading, as "ei" has many other pronunciations, as in, for
instance, "height", "heifer", and "forfeit".  The rule also fails to
apply to names (Sheila, Keith, Leigh, etc.).
"I before E":  Properly applied, the rule is a very useful guide for
people who are not naturally excellent spellers; those who are may
look out for themselves.  To an RP speaker, the exceptions in common
use are very few:  they are "seize", "inveigle", "caffeine",
"protein", and "codeine".  (The last three were originally
pronounced as three-syllable words.)  Other dialects pronounce a few
other -ei- words with /i:/, making extra exceptions:  "either" and
"neither" (RP vowel: /aI/, as in "pie"), "geisha" and "sheik(h)"
(RP: /eI/, as in "say"), and "leisure" (RP: /E/, as in "get").  (Of
course, derivatives of the above words, such as "seizure",
"decaffeinate", and "sheik(h)dom", are spelled similarly.)  There
are many exceptions in Scots, so speakers with a large Scots
vocabulary may as well give up on this rule.  The vowel in "weir"
and "weird" is usually quite different, as comparison of "weird" and
"weed" will show; for most speakers, "weird" has a diphthong.
"except after C":  Fowler, who called the rule "very useful", noted:
"The c exception covers the many derivatives of Latin capio
[= "take"], which are in such common use (receive, deceit,
inconceivable; cf. relieve, belief, irretrievable) that a
simple rule of thumb is necessary."  For most Britons, /i:/ after C
is always "ei" rather than "ie", except in "specie" and "species".
Americans generally pronounce -cies and -cied in words derived from
-cy endings (e.g., "fancies" and "fancied" from "fancy") with /i:/
rather than /I/, making these words exceptions.  Still, few people
have any difficulty pluralizing -y, so such speakers should still be
able to extract some value from the rule, by the application of a
little common sense.
     [See an American's view of the i-before-e rule.]