I would like to understand by what rules I should know when the consonant in the root of a word should be doubled and when it should not. I understand doubling rules resulting from adding suffixes like in "swimming", "knitting", "recalled"; and from other verb conjugation like in "bitten".

But I do not understand general rules applicable to the roots of the words. In particular, by what rules do we spell the following:

"necessary" - with one "c" rather than two and two "s" rather than just one.

"suppose" - with two "p" rather than one and one "s" rather than two.

  • 1
    Swimming and knitting have a doubled consonant because otherwise we'd expect them to rhyme with rhyming and lighting. Recalled isn't an issue, because call already has a double l. Necessary only has one c because we never double up that letter. Suppose could have been different - the double p is presumably only there for etymological reasons. – FumbleFingers Apr 11 '15 at 22:28
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    There aren't really any "rules". Probably someone has a list of factors which might suggest going one way or the other, but English has such a varied past that they will not be very reliable. – Hot Licks Apr 11 '15 at 23:09
  • @Fumble What do you mean "only" etymological reasons? Keeping the hysterical porpoises in stitches is just about all we've got in English! Anyway, most of those words have good reasons for their spellings, even if you do not understand them. And in this case, that answer is Latin, just like in occurrence and separate. – tchrist Apr 11 '15 at 23:19
  • This question may be better on English Language Learners (if it hasn't already been answered earlier). – Kris Apr 12 '15 at 10:26
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    @Araucaria: My bad. I should have said we never double up when it's a soft c. – FumbleFingers Apr 12 '15 at 12:52

There aren't any simple "rules," but here are two factors that may help you remember where double consonants occur in uninflected words in modern English spelling.


This first part doesn't strictly apply to the "roots" of words, but there are a set of prefixes derived from Latin that often cause the following consonant to be doubled. These prefixes usually come from a related preposition that ended in a consonant, but when used as a prefix this consonant assimilated to the next consonant in the word.

This explains the doubled letter in "suppose":

  • suppose: related to Latin supponere, from sub + ponere

and also in many other words:

  • abbreviate, attract, affirm, accommodate, accept, acquire, addiction: the prefix in these is related to the Latin preposition ad, which was very vague but had a meaning something like "to" or "towards"
  • illegible, irreverent, innumerable: the prefix in all these is from Latin in-, meaning "un"
  • collection, correction, connection, commission: the prefix in all these is related to the Latin preposition cum, meaning "with"
  • interrupt: the prefix is from Latin inter "between"

This means that if you can recognize or guess the identity of a Latin prefix in a word, you may be able to predict fairly accurately if it is spelled with a doubled consonant.

"Necessary" is also derived from a Latin word with a doubled consonant, but this was not due to assimilation of a prefix, so there isn't really any way to deduce the spelling of this word unless you know Latin.


In some cases, the pronunciation of a word can give you some clues about how part of it should be spelled.

With the word "suppose", if you know that it is pronounced with the sound /z/ rather than the sound /s/, and that it has a long "o" sound /oʊ/ rather than a short one /ɒ/, you can also make a fairly good guess based on these facts that it is spelled with a single "s" rather than "ss". This is not a failproof "rule" (there are some words spelled with "ss" but pronounced with /z/, although not very many, such as "possess," "dessert," and "scissors") but it may help you to remember the correct spelling.


It may be beneficial for you to learn Latin roots, prefixes and suffixes and your answer may become more clear.

For the word "necessary", the root is "cess". It's relatives are cede and ceed. They all share the meaning of "to go, go away, withdraw, or yield". The prefix "ne" is related to "not". Literally it means "do not yield". The suffix to this word is "ary" which means "having to do with", and makes adjectives (also nouns, but in this case adjective works).

As far as your spelling question: The root is created as "cess", therefore, it is spelled that way.

In the word "suppose" - "pose" - The o is long because of the silent e. No doubling is necessary. The reason for doubling a consonant in words is to keep the vowel sound short. "sup" is a chameleon prefix. A chameleon prefix is one where it changes itself from the original prefix because of "euphony" - or in simple terms, it sounds better. "sup" is part of the "sub" prefix family. Sub means "below or under". "Subpose" sounds awkward, in other words. The "b" changes to "p" when the syllable (root/baseword) after it begins with a p.

If you look up chameleon prefixes in Google, you will find a great deal of info about them. You can study the prefix families one at a time to gain more insight.

Hope this helps!


Instead of "rule", think "pattern." Spelling evolved, not to follow rules, but to create meaning for people who already know and speak the language.

Doubling is mainly lexical. That is, doubling generally occurs in the base of an English word. It is a way of adding stress to the base and/or preserving the quality of short vowels.

The general pattern is that the last letter of a base is doubled if:
a) the added suffix begins with a vowel
b) the base ends with a single consonant letter preceded by a single vowel letter.
c) the stress IN THE FINAL WORD is on the vowel immediately preceding the suffix.

Certain letters never double, like w (already is a double-u) and x (two phones).

re + fer + ed --> referred the base is <fer> and doubles because <ed> is a vowel suffix, has the VC pattern, and the stress in the final word is on the <fer>.

re + fer + ence --> reference the base is <fer> and does NOT double, even though it has a vowel suffix and <fer> has the VC pattern, because the stress in the final word is one the <re>.

As mentioned above, sometimes a "double" consonant is not actually doubled, it is just the same letter ending one morpheme as the beginning of the next.
For example: mis + spell --> misspell
This is NOT a doubled <d>

When <-le> is acting as a suffix (it often does not) in English, it acts as a vowel suffix and forces doubling.

Vowel suffixes that begin with the letter <i> do not usually force doubling, except <ing> which always does.

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