The following rule (or 'rule', this being English) is sometimes quoted:

If a word has two or more syllables, double the final consonant when adding a suffix if and only if the final syllable is stressed in speech.

(There's also constraints about not doubling h, j, q, v, w, x, y (here), but that's not relevant in this case.)

So for example we have

begin \bi-ˈgin, bē-\ → beginning
prefer \pri-ˈfər\ → preferred


listen \ˈli-sᵊn\ → listening
happen \ˈha-pən, -pᵊm\ → happening.

By that logic, we should have

histogram \ˈhi-stə-ˌgram\ → histogramed, histograming.

The trouble is, that's mostly not what people actually do; see the google books Ngram, below. Moreover, Wiktionary says that it is histogrammed/histogramming (here) .

Unfortunately, the major dictionaries do not list histogram as a verb; in particular, the OED doesn't. But in the sciences, people do use it—both with the doubling of the m (here) and without (here). However, the double-m version is 10-20 times more common, according to this google books Ngram:

enter image description here

(A very similar Ngram is obtained for histogramming,histograming.)


  1. Did I state the rule (or 'rule') about the consonant doubling correctly? Here is an example of how simple, often-repeated rules may in reality be simplified versions of more complex actual rules: the source I linked above (as well as many others) says that for single-syllable words, the final consonant is doubled if the vowel is short. But according to John Lawler (here), the actual rule is a bit more convoluted: if the vowel was short in Middle English (/ɪ ɛ æ ɔ ə/) and it uses only one vowel letter and it's in a syllable ended by a consonant, then you double the consonant in spelling. Is there a similarly more complicated rule for multi-syllable words? If so, what does it say about histogramed/histogrammed ?

  2. Imagine you had to use the past tense of histogram in a text. What would you write?

(3. What was this 'histogramming craze' in the early '80s?)


The Free Dictionary has the following discussion:

Exception 1: Doubled consonants in unstressed syllables

Note that there are several words that have primary emphasis on the first syllable but have doubled consonants when taking vowel suffixes. Most of these have a secondary stress on the last syllable, which might be part of the reason why their final consonants are doubled, but this is not always the case.

The situation is made more difficult by the fact that many of these words have variant or accepted alternative spellings in which the final consonant isn’t doubled, and the preference for some of these variants often comes down to regional dialect. This leads to confusing spelling decisions such as kidnaped vs. kidnapped and worshiped vs. worshipped. Unfortunately, we just have to memorize these exceptions:

crystal \ˈkri-stᵊl\ → crystalline, crystallize (but also crystalize; crystalline has only one spelling)
input \ˈin-ˌpu̇t\ → inputted, inputting
kidnap \ˈkid-ˌnap\ → kidnapped, kidnapping (in AmE also kidnaped, kidnaping)
program \ˈprō-ˌgram, -grəm\ → programmable, programmed, programmer, programming (but also programed, programing)
worship \ˈwər-shəp also ˈwȯr-\ → worshipped, worshipper, worshipping (in AmE also worshiped, worshiper, worshiping)

  • 1
    I would go with the short vowel-double consonant rule. "Histogramed" looks almost like it would be pronounced with the "a" as a diphthong eɪ̯. I would use the double m to make the "shortness" of the "a" clear. I feel the reason happen and listen escape this doubling is that their e's are schwas (ə), not because they are unstressed. That's why I would write "focussed", as the u in focus is more a ʊ than a schwa, but that's just my personal feeling.
    – Tim Foster
    Commented Jan 21, 2019 at 11:31
  • I would guess mm in UK, and m in US. I do know that program is used in the US but programme in the UK. Note: the OED does not show histogram verb at all, only noun.
    – GEdgar
    Commented Jan 21, 2019 at 18:04

1 Answer 1


Consonant doubling can occur before the verb inflectional suffix -ed even when the verb does not have a primary stress on the last syllable of its base form. There isn't really any simple rule for when this happens. You can see some attempts at formulating more complicated rules in Alex B.'s and Patricia M's answers to the following question: "Focussed" or "focused"? Rules for doubling the last consonant when adding -ed

The spelling histogrammed is likely based at least in part on analogy with the more frequent word programmed. There was a previous question about the forms of that verb: “Programming” versus “programing”: which is preferred? I use -mm- spellings for these words and also for diagrammed and anagrammed.

The use of double consonant spellings for -gram verbs is probably related to their pronunciation, and possibly to their etymology.

  • They are pronounced with an unreduced vowel /æ/ in the last syllable. In some theories of English stress, this implies that the last syllable has some kind of stress (even though it doesn't have the primary stress).

  • The Greek source of -gram, -γραμμα, has a double consonant. The spelling programme is used in British English in most circumstances.

I think the quotation from The Free Dictionary confuses different kinds of examples that would be better dealt with separately. The rules for doubling consonants before the inflectional suffixes -ed and -ing shouldn't be expected to govern the use of doubled consonants in all other kinds of words. In Latinate words, double consonants occur fairly often after unstressed vowels, usually for etymological reasons.

The double -ll- in crystalline and crystallize is probably related to etymology: -ize is a suffix that doesn't only attach to English words, but also to bound Latinate roots (e.g. anglicize). I wrote an answer to a question about the spelling alternation between -our and -or- in words like vapour, vaporise that talks about the general principles for spelling words ending in the suffix -ize (-ise).

Similarly, the spelling of the noun cancellation is based on etymology and for most users of American English, it does not correspond to the spelling of the inflected forms of cancel (canceled and canceling).

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.