The word bicycle is pronounced /'baɪsɪkəl/ (bahy-si-kuhl), like sickle. However, the words unicycle and motorcycle both have the -cycle pronounced as /-'saɪkəl/ (sahy-kuhl). Is there some sort of reason for this, or is this just a vagary of English pronunciation?
Although such variation could be the result of things like when the word was borrowed into the language, this variation is probably due to the prosodic structure of the words; we get different vowel sounds because of the way that stress influences vowel quality in English.
In English, unstressed vowels are generally reduced. Take the word record for example.
Now for bicycle and unicycle:
The reason boils down to English prosody and stress patterns.
First, a general observation that the vowel [aɪ], which is the first vowel in cycle, very rarely occurs in unstressed syllables. Unstressed syllables that would otherwise contain this vowel tend to reduce it to [ɪ] or even [ə], as nearly all English vowels are so reduced when they occur in unstressed syllables. From this we can infer a general pattern that the vowel in cycle will only be pronounced as [aɪ] as long as the vowel is stressed.
The second observation is that both motorcycle and unicycle consist of a pair of trochees: MO-tor-CY-cle, U-ni-CY-cle. The primary stress in both words falls on the first syllable, but the secondary stress falls on the first syllable of -cycle. In this context the vowel retains its full pronunciation.
Bicycle, however, has only one syllable before the -cycle, and the primary stress falls on this syllable. English does not allow two stressed syllables in a row in native words, which means that the second syllable of bicycle has no secondary stress. In turn, this means that the vowel [aɪ] is reduced to just [ɪ] in this context.
There are a few exceptions to this rule about two stressed syllables in a row, but they are all compounds or neologisms: fly-by, cry-baby. And in fact, the oldest spelling of the word bicycle is bi-cycle, where the hyphen is meant to indicate that the word is a compound and suggests the pronunciation b[aɪ]-c[aɪ]cle. But as the word bicycle became more common, the word was adapted to the native stress pattern, requiring reduction of the vowel in the second syllable.
protected by RegDwighт♦ May 19 '11 at 15:31
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