Note: if you can't read ASCII IPA notation, go learn it. It's not hard. The sounds made by most consonant symbols are obvious, though this week's column contains some exceptions, and there aren't many common vowel symbols to learn.
Several months ago I deconstructed the idea of verbs and nouns; now I'm going to go deeper, and show that not even vowels are what they seem.
Those of you who grew up in America are probably saying, "I know what a vowel is! It's a, e, i, o, u, and sometimes y!" (Some may instead say "...and sometimes y or w!", having been taught that the w in "cwm" acts as a vowel.) But that's only the orthographic definition, a description of how vowel sounds are written down, and is thus irrelevant to linguists. Many people never quite understood the "and sometimes y" part; that's because that part mixes spelling with sound. That is, the letter y (like many letters) can represent several different sounds; it's a vowel only in places where it sounds like a vowel (like the /i/ at the end of 'only'). To further confuse the issue, there are many more than five vowel sounds in English, which means that each vowel letter is used to represent multiple sounds.
So forget any ideas you may have about vowels as letters; for the rest of this column, "vowel" means "vowel sound."
Now that we've eliminated one definition of "vowel," let's look at another: a vowel is the most prominent sound in a syllable; it's the nucleus around which a syllable is built.
But what exactly is a syllable? My dictionary says that a syllable is a unit of sound, generally larger than a phoneme, and that a syllable is composed of a vowel (or a syllabic consonant) plus optional preceding and following consonants.
And to round out the circularity, a syllabic consonant is defined as a consonant which can form a syllable without the help of a vowel.
In other words, all syllables are based on vowels, except those which are based on consonants; and a vowel is the sound that a syllable is based on, unless it's a consonant. I hear the gostak calling...
Luckily, there's yet another definition of "vowel" which clears up a little of the murk: a vowel is a speech sound which isn't blocked or noticeably constricted (to the point of making a friction sound) by vocal articulation. (If you want to distinguish between this phonetic kind of vowel and the above phonological definition, you can call a phonetic vowel a "vocoid." But nobody but a phonologist will understand you.)
So, a syllable (the word is from Greek syllambanein, "to gather together") is a unit of sound that's constructed around a speech sound that's made with an unrestricted air flow. Of course there's more to syllables than that; even linguists may have a hard time defining the term usefully. For instance, why should a basic linguistic unit require a certain kind of sound to be present? Michael suggests one possibility: vowel sounds are much easier for infants to make than consonants (which require greater articulation, and thus better fine motor control), so the sounds become a basic part of a language.
Now we can examine the idea of a "syllabic consonant." (The term is due to linguists Noam Chomsky and Morris Halle—these consonants were formerly called "vocalic.") Note that in American pronunciation of words like "button" (especially when pronounced with a glottal stop (/?/) in the middle rather than a /t/ or /d/ or flap) or "fire," the final syllable sounds like it contains no vowel—/'b@? n-/, /'faI R/. (In ASCII IPA, syllabic l, m, n, and r are denoted /l-/, /m-/, /n-/, and /R/, respectively.) The traditional description of this phenomenon has been that the last syllable consists of a schwa sound and a consonant: /'b@? @n/, /'faI @r/. But that schwa is arguably just a notational convenience, a way of avoiding exceptions to the rule that all syllables must contain vowels. If instead we relax that rule and say that some syllables can be built on sonorant consonants that behave somewhat like vowels, we can use a different notation. There's much debate among experts over which of these notations makes more sense, but one can take the middle ground and say that they're pretty much interchangeable, that it doesn't really matter which way you write it.
(Once you allow syllabic /R/, you can avoid vowels altogether in IPA transcriptions of words like /bRd/ or /wRd/—or you can redefine syllabic consonants as vowels for the purposes of easy discussion.)
Now that we have a slightly better idea of what a syllable is, how do you tell where a syllable starts and ends? Clearly the division between syllables comes between vowels (and/or syllabic consonants), but where between? Bear in mind that hyphenation rules are not the same as syllabification rules—in my dictionary, for instance, good places to hyphenate a word are marked with bullets in the main entry, while syllables are separated by hyphens in the pronunciation. Confusing, no? As far as I can tell, deciding what consonants go in what syllable is largely a matter of deciding what linguistic theories you want to support; there doesn't seem to be a hard-and-fast rule on the subject, other than "consult the dictionary." One linguistic approach involves starting with the vowel and working backwards until you find a sound that doesn't work in the syllable, but this approach isn't perfect. Fortunately, one rarely needs to know exactly where the division between syllables falls.
Thanks to Michael Bernstein for answering a lot of questions and providing most of the information in this column.