Do you say car-a-mel or car-mel? Is your "fire" closer to fah-yer or fayr? There is a group of words in English that can be pronounced with two different syllable structures, depending on dialect, personal preference, or context of use. While many will insist that one or the other is incontrovertibly correct, there is usually no real basis for pronouncements on the one true syllable structure. Sometimes two things can both be correct. If you need a better authority than me on that, many dictionaries accept both pronunciations for all the words discussed below (e.g., Merriam-Webster).
What's more interesting, though, than fighting about who's right is understanding why these differences arise. Let's look at the three processes that result in syllabically ambiguous words.
1. DIPHTHONGS, R'S, AND L'S
One or two syllables: fire, tire, hour, liar, buyer, flower, drawer, layer, loyal, royal, file
All of these words have one- and two-syllable pronunciations. What do they have in common? They all have a diphthong followed by an r or l.
At least in their one-syllable versions. A diphthong is a glide from one vowel to another that takes place within one syllable. For example, the vowel sound in "hour" glides from "ah" to "oo." A diphthong is not always represented in the spelling of a word. The vowel sound in "fire" glides from "ah" to "ee."
The sounds that make up the second part of the diphthongs "oo" and "ee" can also serve as consonants when they start a syllable. "Win" starts in the "oo" position, but there, it is the consonant w. "Yes" starts in the "ee" position, but there, it is a y. (In technical terms, w and y are semivowels whose vowel/consonant status depends on whether they are in the nucleus of the syllable or at the edge of it.)
Sometimes the end of the diphthong becomes w or y, forming a second syllable. Hour becomes ah-wer and fire becomes fa-yer. This process also works in reverse. Sometimes a w or y moves over to join the vowel before it. Flo-wer becomes flour.
This kind of indeterminacy is all over the place. Think about "mower," "shower," "oil," "hair," "while," or any other diphthong followed by l or r. Think of a one or two syllable pronunciation for each of them. Even if you think one of them sounds totally weird, you can imagine someone saying it.
One or two syllables: orange, poem, crayon
Two or three syllables: caramel, mayonnaise, family, chocolate, camera, different, separate, favorite
Three or four syllables: interesting, comfortable
Four or five syllables: laboratory
These words all have a syllable which is often left out of the pronunciation. When we cut a sound out of the middle of a word, it's called syncope (a three syllable word, sin-ko-pee). O-range becomes ornge, car-a-mel becomes car-mel, in-ter-es-ting becomes in-tres-ting. This pruning of syllables doesn't happen in some random, haphazard fashion. If a vowel gets chucked, it will be before an r or l (those guys again!) or in some cases a nasal (m or n). It will also be from an unstressed syllable. So the American LA-buh-ra-to-ry becomes lab-ra-to-ry, while the British la-BO-ra-to-ry become la-bo-ra-try.
Two or three syllables: realtor
Three or four syllables: mischievous
When we stick a sound into the middle of word, it's called epenthesis. A few words gain extra syllables this way. Do you say mis-chi-vous or mis-chee-vee-ous? Real-tor or real-a-tor? Epenthesis usually happens in order to make something easier to pronounce — because some words can be as tricky as a mischievous realtor.