Detecting Diphthongs in Spanish
Diphthong means double sound. The Spanish word is diptongo (deep-tohn-goh). Diptongos are the combination of two vowels, from the Spanish-speaking point of view. For instance, the vowels i and o combine to make io as in patio (pah-teeoh) (courtyard or patio).
Diptongos are always made up of a weak and a strong vowel. Calling vowels “weak” or “strong” is a convention of the Spanish language. The convention comes from the fact that the so-called strong vowel is always dominant in the diphthong. To the Spanish speaker, i and u are weak vowels, leaving a, e, and o as strong ones.
To visualize this weak or strong concept, consider a piccolo flute and a bass horn. The sound of the piccolo is definitely more like the Spanish i and u, while the base horn sounds more like the Spanish a, e, and especially o.
Joining the weak to the strong
Any combination of one strong and one weak vowel is a diptongo, which means they belong together in the same syllable. In fact, they’re not only together, they’re stuck like superglue; they can’t be separated.
In the diptongo, the stress falls on the strong vowel. An accent mark alerts you when the stress falls on the normally weak vowel. In the combination of two weak vowels, the stress is on the second one.
Try these examples of diphthongs:
bueno (bvooeh-noh) (good)
cuando (kooahn-doh) (when)
fiar (feeahr) (sell on credit)
fuera (fooeh-rah) (outside)
suizo (sooee-soh) (Swiss)
viudo (bveeoo-doh) (widower)
Separating the strong from the strong
When two strong vowels are combined, they don’t form a diphthong. Instead, the vowels retain their separate values, so you must put them into separate syllables. Here are some examples:
aorta (ah-ohr-tah) (aorta, just as in English!)
feo (feh-oh) (ugly)
marea (mah-reh-ah) (tide)
mareo (mah-reh-oh) (dizziness)