At first glace, the Spanish phonemic vowel system seems oversimplified, with just the vowels /a/, /e/, /i/, /o/, /u/. Spanish makes no distinction between the [ε] sound in the English 'bet', and the [e] sound in 'bait'. Though both of these sounds occur in say, estrella, they are both perceived as /e/, since these two sounds are allophones in Spanish. There are a few exceptions, but they are rare and occur in dialect.

However, Spanish has an assload of diphthongs, many more than in English (English only has /au/ ('mouse), /ai/ ('kite'), and /oi/ ('boy') as full diphthongs). In Spanish, the word piano is two syllables, not three. It is pronounced /pîa-no/ (I am using circumflexes because mine and most people's browsers suck at displaying IPA). These diphthongs are formed by combining a 'weak' vowel /i/ or /u/ with a 'strong' vowel /a/ /e/ or /o/. The weak vowels become deslizadas, meaning they 'slide' into or out of the other vowel. There are three kinds, creciente 'increasing', decreciente 'decreasing', and antecreciente uh, 'not...creasing'. Here are all of them (there are 14 in all):

  • /îa/... 'piano' /pîa-no/ (sounds like 'ya' in (English)
  • /îe/... 'serpiente' /ser-pîen-te/ (sounds like 'yen' in English)
  • /îo/... 'unión' /u-nîon/ (sounds like English 'yo')
  • /ûa/... 'agua' /a-gûa/ (sounds like English 'wah'
  • /ûe/... 'agüero' /a-gûe-ro/ (sounds like English 'wet')
  • /ûo/... 'antiguo' /an-ti-gûo/ (sounds like English 'woe')
  • /aî/... 'hay' /aî/ (sounds like English 'I')
  • /aû/... 'causa' /caû-sa/ (sounds like English cow)
  • /eî/... 'reina' /rreî-na/ (sounds like English 'hey')
  • /eû/... 'deuda' /deû-da/ (has no real English equivalent, but is kinda like saying 'eww')
  • /oî/... 'hoy' /oî/ (like English 'soy')
  • /oû/... (doesn't occur in native words, but trust me, it does exist, and sounds like English 'know)
  • /uî/... 'huir' /ûir/ (like English 'we')
  • /iû/... 'viuda' /bîu-da/ (like English 'you')

Also, there are triphthongs, which are much less common in individual words (though they do occur, as in 'buey' /bûeî/). They are ...*ahem* ... /îaî/ /îaû/ /îeî/ /îeû/ /îoî/ /îoû/ /îuî/ /ûaû/ /ûaî/ /ûeû/ /ûeî/ /ûoû/ /ûoî/ /ûiû/. Where you will see many triphthongs, as well as a bunch of diphthongs is between word boundaries. Unlike English, Spanish does not stop at all between words, and indiscriminatly joins syllables whether they belong to the same word or not, according to Spanish rules for syllables. Here are some examples:

  • Alemania y Francia. /a-le-ma-nîaî-fran-sîa/
  • el lado único /el-la-doû-ni-ko/
  • Gloria y Pepe huyeron /glo-rîaî-pe-peû-îe-ron/

Of course, there are things called antidiptongos, which are exactly what they sound like. They are when a diphthong would normally be formed, but isn't, and are marked by an acute accent on the weak vowel. An example is país, which is /pa-is/ and not /paîs/. When the accent occurs on the strong vowel, it simply means that the entire diphthong is stressed. it does not break up the diphthong. An example is comió, which is still /ko-mîo/, not /ko-mi-o/.