Why are certain words pronounced with diphthongs on their own but with monophthongs in compounds? For example:

Words pronounced with diphthongs on their own: Michael, Christ, wise, drive

Their pronunciations with monophthongs in compounds: Michaelmas, Christmas, wizard, driven

All of these changes occur in stressed syllables. Compare that of cycle and bicycle, tricycle which occurs in unstressed syllables.

P/s: Just to be clear, I added the "historical-change" tag because I suspected this phenomenon had something to do with the Great Vowel Shift.

  • 21
    For what it's worth, I generally hear the Y in cycle and bicycle pronounced differently, in basically the same way is Christ/Christmas.
    – aslum
    Jun 1 '16 at 16:55
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    'Michaelmas'? Sounds like a Michael Scott-ism...
    – TylerH
    Jun 2 '16 at 18:33
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    @aslum: The OP is not saying that the <y> is pronounced the same way in bicycle as in cycle; rather, (s)he's saying that that pronunciation difference is to be expected, since the <y> is unstressed in bicycle (whereas in the pairs (s)he's asking about, the corresponding syllable is stressed in both words).
    – ruakh
    Jun 3 '16 at 6:05
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    @ruakh Indeed. I checked and a question regarding "cycle/bicycle" had been asked. I just wanted to make clear that I didn't ask that same question again. Jun 4 '16 at 13:34
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    @O.M.Y. it's the same thing, other than the fact that the /aɪ/ that becomes a /ɪ/ is spelled with a "y" rather than an "i".
    – hobbs
    Jun 4 '16 at 22:31

Short answer

The PRICE vowel that we hear in the word wise, /waɪz/, has a systematic relationship with the KIT vowel which we hear in the word wizard, /'wɪzəd/. As we add syllables to the base of a word in English, we tend to reduce the length of the vowel in the base. This is so that we can accommodate the new syllables and still preserve the perceived stress timed rhythm of English. When we add syllables to a base word containing the PRICE vowel, the vowel is very likely to change to a KIT. Other pairs of long and short vowels have this same type of relationship in English.

Full answer

What the Original Poster is observing here is a side-effect of the way English organises stressed syllables in connected speech.

English is a 'stress-timed' language. What this means is that the syllables in English utterances do not come at regular intervals in the way that they do in Japanese for example, or in Spanish. Instead English utterances give the impression that the stressed syllables come at regular intervals. In actual fact this is not strictly what's happening, in the sense that although they give this impression, the stressed syllables do not occur at strictly regular intervals at all.

The upshot of this is that the following utterances, for example, will take roughly the same amount of time to pronounce in English:

  • fish, peas, beans, rice.
  • fish and then some peas and a banana and a casserole.

The first utterance there has only four syllables, but the second has fifteen. However, in normal relaxed speech, these sentences will have approximately the same duration. This is because they each have four stressed syllables:

  • fish, peas, beans, rice.
  • fish and then some peas and a banana and a casserole.

Now, if you're a native speaker, if you tap out the stressed syllables as you say the two utterances, you'll realise that the stressed syllables seem to come at regular intervals, regardless of what other material comes in between them.

English has a system for enabling this to happen. One part of this system is that many grammatical words have two forms. They have a strong form which we use if these words are stressed (or stranded). They have a weak form which we use if they are not stressed. So for example, the strong form of can is /kæn/ and the weak form is /kn/ or /kən/. You will be able to hear the difference in the following examples:

  • I can dance.
  • I can dance.

What you will notice is that these weak forms have a reduced vowel, most usually a schwa, /ə/. This vowel is easy to pronounce very quickly because it does not require any large movements of the articulators.

Another effect that we find is that a given stressed syllable will become shorter when more unstressed syllables are added. So the if we compare the /mæn/ ('man') in the word man and the /mæn/ in the word manager, we will find that /mæn/ is much longer in the first word than in the second. Compare:

  • He's a man.
  • He's a manager.

The reason for this is that with the word manager, we need to be able to squash the rest of the word in before the next stressed syllable arrives. Reducing the length of the vowel in /mæn/ enables us to squish in the next two syllables without radically increasing the length of time it takes to say the word. This is known as rhythmic clipping.

Within words themselves we can see processes similar to the ones above at work. English has families of vowels. In British English we can notionally divide these families according to the perceived length of the vowel. So in one group we have the long vowels, /i:, u:, ɑ:, ɔ:, ɜ:/ (as in bead, booed, bard, board, bird), and the diphthongs. In the other we have the 'short' vowels, which include, amongst others /ɪ, e, æ, ɒ, ʌ/ (as in bid, bed, bad, bod, butt).

Now, there seems to be a systematic relationship between many long vowels in English and other specific short vowels. If you speak English, these qualities will seem to be logical. In fact, they aren't. In terms of the actual sound there is almost no phonetic relationship between the long vowels and their short vowel counterparts in modern English. For example, the vowels in the words weight and bad are not very similar. We represent these sounds by the symbols: /eɪ/ and /æ/ respectively. However, these vowels have a very close relationship in the language. For example, the following words have the /eɪ/ vowel:

  • grateful
  • sane
  • inflame

The following words, on the other hand, even though they have the same root, usually have the vowel /æ/:

  • gratitude
  • insanity
  • inflammatory

This change from long to short vowels usually happens when there are extra syllables added to the base or root of the word. The more syllables there are in a word the more short vowels and the fewer long vowels we are likely to see. We can think of this as a kind of phonological rhythmic clipping. It helps to reduce the amount of time needed to say that syllable in order to accommodate the other unstressed syllables. The following long and short vowels have this same relationship:

  • eɪ / æ
  • i: / e
  • aɪ / ɪ
  • əʊ / ɒ
  • aʊ / ʌ

These relationships can be seen in the following pairs of words respectively:

  • chaste / chastity
  • penal / penitentiary
  • wise / wisdom
  • joke / jocular
  • south / southern

The Original Poster's Question

The /aɪ/ diphthong that we find in words such as Michael, Christ and wise has a phonological relationship with the short vowel /ɪ/ in English. Because English is stress timed, it has systematic methods for reducing vowel lengths in order to accommodate unstressed syllables without radically disrupting the natural rhythm of the language. When we add syllables to base words containing the PRICE vowel, /aɪ/, it is likely to change to a KIT vowel /ɪ/. This is what we see in the Original Poster's examples:

  • 'maɪkl /'mɪklməs
  • 'kraɪst / 'krɪsməs
  • 'waɪz / 'wɪzəd
  • 'saɪkl / baɪsɪkl

Transcription note

I have used a standard British English transcription, as used by John Wells in Longman Pronunciation Dictionary

  • 72
    This is absolutely fascinating. I'd never heard of, or noticed, the regular timing of the stressed syllables but it's absolutely there once you start listening. It's most obvious in emphatic speeches, i think, of politicans for example: it even enables them to bang their fist along with the stresses. Jun 1 '16 at 12:47
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    Absolutely fantastic answer. Also, for someone wanting to hear the difference between syllable and stress timing within a language, compare Brazilian Portuguese (strongly stress timed) and European Portuguese (strongly syllable timed). Jun 1 '16 at 13:19
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    I like that you have the disclaimer about the "regular" intervals not being regular. But then you go ahead and say that "fish, peas, beans, rice" and "fish and then some peas and a banana and a casserole" have "the same duration" in "normal relaxed speech"; I'm very dubious of this. The second one definitely seems longer when I say it to myself. Isochrony is a complicated topic; there is an interesting answer on Linguistics SE by Robert Fuchs that suggests that it mainly applies to vowel durations, not to the duration of whole utterances.
    – herisson
    Jun 1 '16 at 16:06
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    @sumelic Try fish, peas and a banana and a casserole. That's 50% of one list and 50% of the other. Try and do that so that the third and fourth stresses don't come out perpetually at the same intervals as the first two syllable whilst saying it naturally. It's well nigh impossible. Try it! Jun 1 '16 at 16:33
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    "If you speak English, these qualities will seem to be logical. In fact, they aren't" - I feel like every answer on this site should include this somewhere! Jun 2 '16 at 23:41

Etymological explanation:

Christmas is a short form of 'Christ's mass'.

Old English Cristes mæsse: /ˈkris.tes ˌmæs.se/.

Middle English Cristemasse:

/ˈkristismas(ə)/ or /'kristismɛsə/ -> /krist(ə)mas(ə)/ or /'krist(ə)mɛs(ə)/ -> /ˈkrismas/ or /ˈkrismɛs/

Modern English Christmas: /ˈkrɪs.məs/

Etymologically, Christmas never had the PRICE vowel (/aɪ/) so it cannot lose something it never had.

As for Christ, it was pronounced /krist/ in Old English and /kri:st/ in Middle English. The vowel in Christ lengthened by undergoing vowel changes in Middle English but for some reason Christmas didn't go through those vowel changes.

Later on, the long vowel /i:/ in Christ was affected by Great Vowel Shift and shifted to /aɪ/.

Phonological explanation:

If you think that Christmas is derived from Christ by adding the suffix -mas to Christ, then the diphthong in Christmas laxed because of a process called Trisyllabic laxing.

Trisyllabic Laxing:

It's a process where the vowel in a stressed syllable is shortened if two (or more) syllables follow. If the stressed vowel is in at least* the penultimate syllable (third-last syllable of the word) then it must be lax.

(*I say at least because the tense vowel in some words follows more than 2 syllables but trisyllabic laxing still occurs.)


  • Profane, profanity --- /prəˈfn/ -> /prəˈfæn.ə.ti/
  • Sincere, sincerity --- /sɪnˈsɪə/ -> /sɪnˈser.ə.ti/
  • Impede, impediment --- /ɪmˈpd/ -> /ɪmˈped.ɪ.mənt/
  • Divine, divinity --- /dɪˈvn/ -> /dɪˈvɪn.ə.ti/
  • Michael, Michaelmas --- /mkl/ -> /mɪkəlməs/
  • Profound, profundity --- /prəˈfnd/ -> /prəˈfʌn.də.ti/
  • Provoke, provocative --- /prəˈvəʊk/ -> /prəˈvɒk.ə.tɪv/

The above words have a very regular pattern of vowel change which is summarised below:

  • /eɪ/ -> /æ/
  • /ɪə/ -> /e/
  • /iː/ -> /e/
  • /aɪ/ -> /ɪ/
  • /aʊ/ -> /ʌ/
  • /əʊ/ -> /ɒ/


In the Modern English, there are systematic exceptions to the process, such as in words ending in -ness (like mindfulness, loneliness etc). There are also occasional, non-systematic exceptions such as obese, obesity (later borrowings).

  • Obese, obesity --- /əʊˈbs/ -> /əʊˈb.sə.ti/

  • Private, privacy - Trisyllabic laxing applies in British English but not in American English --- /ˈpr.vət/ -> BE: /ˈprɪv.ə.si/, AE:/ˈpr.və.si/

  • Code, codify --- /kəʊd/ -> BE: /ˈkəʊ.dɪ.faɪ/, AE:/ˈkɑː.də.faɪ/

  • Some words having the suffix -able. Examples: Signable /snəb(ə)l/, boatable /ˈbəʊtəb(ə)l/ etc.

There are many more exceptions, however.

Origin: Perhaps of multiple origins. Partly formed within English, by compounding. Perhaps also partly formed within English, by clipping or shortening. Etymons: Christ n., mass n.1, -mas comb. form; Christenmas n - OED

Christ Vs. Christmas:

In some cases, trisyllabic laxing appears to take place when it should not have done so. For example, Christ /kraɪst/ vs Christmas /ˈkrɪs.məs/, even though the stress syllable in Christmas is followed by one syllable yet it gets laxed. In such cases, the anomaly is caused by later (historical) sound changes.

Christmas was a three syllable word (stress on first syllable) when Trisyllabic laxing applied. It was Christenmas or Christemas.

Other examples:

  • South Vs. southern: [sθ] -> [ˈsʌð(ə)n], the syllable having the tense vowel is followed by one syllable but Trisyllabic laxing still occurs, it's because of later sound changes. The stress syllable in southern was followed by two syllables when Trisyllabic laxing applied --- /ˈsuːðər.nə/ (/uː/ changed to /aʊ/ because of Great Vowel Shift).

  • Wise vs wizard: wizard also has trisyllabic laxing. Wizard was trisyllabic when TSL applied but I didn't find any reference for the word 'wizard'.

  • Tone vs tonic etc.

(As for the silent T in Christmas, it was once pronounced but during the 17th century, the T was dropped whenever it was preceded by a fricative and followed by a sonorant.)



Christmas was said as krisstmahs while Christ was said as Kreest,the ee sound was the long version of ih so ''I'' in english was once said the way Dutch,Danish etc say it as modern english ''ee''.A word that has one syllable's easier to be given vowel length then ones that have more than one,also y and w sounds tend to fall/merge with the following/previous sound when the the semivowel is followed by a sound that is very created closely in the mouth to where they are eg: y sounds and s/sh/ch and w sounds and r(WRite/sORe/cROissant) also consonants next to each other have a tendency for one of them to fall,since it's easier to pronounce only one of them(french orthography is full of this trend since the orthography was never changed and also cause it depends on the position of the word), now when the great vowel shift happened(that took ages) krisstmas only lost it's t and mahs became mss/muhs Christ went from kreest became krihyst to kruhyst(many irish and canadians still say it like this) to kraahyst(many americans say it like this), some people have it gone further to something along to Krahyst or even Kroyst(many southern brits)

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