Vowels in Spanish

Spanish has five vowels: a, e, i, o, u. 
Three of them are strong vowels (a, e, o), and the remaining two are weak vowels (i, u).
In Spanish the strong vowels are often called “vocales abiertas”, and the weak ones, “vocales cerradas”. But they are also called “vocales fuertes” and “vocales débiles (which is the translation of strong vowels and weak vowels)

It is important to have this distinction clear and to know which group each vowel belongs to, because the combination of the vowels indicates how a word is separated into syllables. See this:

• two strong vowels together: two syllables
• two weak vowels together: one syllable because there is a diphtong
• strong and weak vowell: one syllable because there is a diphtong