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I almost hesitate to ask this, because it is hard to believe no one else asked it; but it isn't showing up in the "similar titles" list.

What is special about 'C' that switches the 'IE' immediately following it?

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It's not true. They don't teach that at schools (over here in the UK) any more. –  Matt Эллен Jul 15 '11 at 15:24
@Matt Ellen - Yet another example of USA education falling behind the rest of the world. :-( –  T.E.D. Jul 15 '11 at 18:13
The rule is not what you state. It is that when you have an /iː/ sound and must choose between the the two spelling “ie” and “ei”, *then and only then is it “ i before e except after c”. It has never ever ever been a general rule without the conditions I gave. The chief exception is weird. –  tchrist Feb 21 '12 at 21:27
The rule is rather unscientific. –  Daniel Harbour Jan 18 at 18:10
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2 Answers

up vote 20 down vote accepted

Basically, English vocabulary is a mix of mostly proto-Germanic and proto-French, the languages in use by the Saxons and Normans respectively during the Norman invasion and occupation of the British isles. To this was added hefty dashes of classical Latin and Greek, and then Romanizations of words from all over as words were borrowed from British colonies and from American immigrants.

Anyway, in German, the rule (when explained to native English speakers) is that when I meets E, the second vowel is the sound of the pair, and is sounded long. So, EI is sounded like "aye", and IE is "ee".

In French, it's not so simple, but usually, IE is "ee" and EI is "ey" (long a). It's really closer in most cases to "eh", but that's far more open than the "eu" or schwa sound that is an unattended "e".

So, from both these languages, when "ie" is a monopthong (or "digraph"; two letters making one sound), it's usually "ee", and then "ei" is normally given its French pronunciation of long "a" or similar (as in "neighbor" or "weigh"), with a few exceptions usually given the Germanic long I.

The mixing in of C also appears French; the word "deceive", for instance, is rooted in the old French deceivre, identical in meaning. The French would use their normal long "a" pronunciation for "ei", but in the transition to modern English it became "ee". Words such as "receive" and "ceiling" also have ties to French, though sometimes, as with "ceiling", the spelling in the other language isn't anywhere close.

So, that's the origin of the rule; when I and E meet to say "ee", both of English's parent languages usually indicate "ie". The "except after c" is because we Anglos butcher the French contribution so badly, and the "or when sounded as 'ay'" is for the rare occasions we get it right.

Now for why it's not such a great rule:

The largest section of exceptions to the full rule, "I before E, except after C, or when sounded like 'ay', as in 'neighbor' or 'weigh'", is when "ie" or "ei" is not a digraph, but instead a diphthong. The word "science", and its various derived words, do not have their "ie" pronounced as long "e" OR long a; it's two elisioned sounds, "eye-eh". Same with "conscience". Similarly, words like "deity" are pronounced "ey-ih", again pronouncing each letter. Most of these are from base Latin or Greek roots instead of French/German.

The second biggest group of exceptions are words that have evolved multiple acceptable pronunciations: "either" can be pronounced "ee-ther" or "eye-ther" depending on dialect. Similarly, "neither", "geisha", "leisure", "weird", etc. all have multiple acceptable pronunciations of the digraph.

Recent additions to the English language, borrowed from other languages, are likely to also be exceptions to the rule; "gneiss" for instance.

Finally, the plural form of a word ending in "cy" such as "fancy" or fluency" is always spelled with "cie" ("fancies", "fluencies").

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Weird can be pronounced w-eye-rd? Odd. +1 for an excellent answer. –  MrHen Jul 15 '11 at 4:37
Geisha can be pronounced geesha? I'm shocked! O_O –  deceze Jul 15 '11 at 5:08
@MrHen: Actually, the alternate pronunciation other that "weerd" would be "wihrd", using an "i" as in "pit". This word comes from the Celtic "weir" which is pronounced "wihr". –  KeithS Jul 15 '11 at 15:15
You’ve made if far too complicated. The rule is that when and only when something is sounded /iː/ and you must choose between “ie” and “ei”, then and only then is the rule to spell it “i before e except after c”, with the chiefmost exception being weird. The -cy > -cies inflection is a good catch, though. –  tchrist Feb 21 '12 at 21:30
@tchrist: The rule only applies in stressed syllables. When the letters ei/ie are used to represent stressed /i:/, ei is used if the preceding letter is c, and ie otherwise (except ‘weir’ and ‘weird’ and perhaps a few others here and there as well). –  Janus Bahs Jacquet Jan 18 at 4:32
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Well, the rule isn't true at all. There are more exceptions to the rule than that follow it.

According to QI, 923 words have cie (against the rule), 23 times more than cei (following the rule).

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I knew it! I knew that silly rhyme was just too good to be true! Why did they dumb things down to me, those patronizing cows of public education! –  Adel Jul 15 '11 at 1:11
Well, I know.. I was being a little bit facetious. But still, they don't stuff our young kids' brains enough. Kids have sponges in their heads. –  Adel Jul 15 '11 at 2:10
But that's not what the rule says. It says it's always "ie" not "ei", but that the rule doesn't hold after "c". It doesn't say "i before e but the opposite way round after c". So it has its limitations (though fewer if you use the version "i" before "e", except after "c", when the sound is "ee" that is common in the UK), but that's not one of them. –  psmears Jul 15 '11 at 8:35
+1 (++) - So glad to see this answer. One thing you don't mention is that the "full" text of the rule has an exception and an exception to the exception tacked on in a desperate attempt to make the rule valid. Even when you do that, the most common i & e word in English (their) doesn't follow the rule. I misspelled "their" for decades because I had that stupid non-rule "rule" beat into me as a kid. –  T.E.D. Jul 15 '11 at 17:49
This answer says nothing about whether this is a good rule of thumb because it completely ignores (a) the probability distribution of words (i.e. maybe words that break the rule are less common than those that follow it) and (b) the number of words that contain "ie"/"ei" not following a "c". –  Aaron Novstrup Jul 16 '11 at 0:25
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