Strong and Weak Vowels – Concept, hiatus and diphthongs

We explain what strong and weak vowels are, how they differ and how they can form diphthong or hiatuses.

strong and weak vowels
The vowels are strong or weak according to the opening of the mouth when pronouncing them.

What are the strong and weak vowels?

According to the phonetics of Spanish, vowels are differentiated into two different categories, depending on the degree of opening of the oral cavity when pronouncing them: on the one hand strong vowels and on the other weak vowels.

These categories coincide, respectively, with the classification used in international phonetics: open or low vowels and closed or high vowels, depending on a criterion that responds to the opening of the mouth and the position of the tongue at the moment of pronouncing them.

  • The strong vowels, then, are those that require a greater degree of openness of the mouth when pronouncing them, and that act as the nucleus of the syllable in which they are found. We refer to the vowels “a”, “e” and “o”.
  • On the contrary, weak vowels They require a considerably smaller opening of the mouth to pronounce, and usually form diphthongs under certain conditions of position and tonicity. We refer to the vowels “i” and “u” (and also, from a phonetic point of view, to “ü” and to the consonant “y” when their sound is vowel, as in the word King).

This phonetic distinction is of importance in the Spanish language, since the possibility will depend on it, as we will see below, of having diphthongs and hiatuses within a word.

Diphthongs and hiatuses

The distinction between weak and strong vowels makes sense in Spanish when it comes to understanding their acoustic junctions (diphthongs) or their syllabic separations (hiatuses).

For a diphthong exists, that is, for two Spanish vowels to be pronounced continuously and form an inseparable part of the same syllable, these vowels must necessarily be:

  • A weak vowel and a strong vowel, in any order, as in the cases of “cielo “,” pleito “,” raudo “or” secuaz “.
  • Two unstressed weak vowels, even if they are the same, as in the cases of “chiita “,” ciudad “or” cuidice”.

On the contrary, hiatuses or diphthong breaks occur when the two contiguous vowels are:

  • Two strong vowels, even if they are the same, as in the cases of “caer “,” leer “,” leatheoez “.
  • A strong vowel and a weak vowel, but the latter with an accent, as in the cases of “mio“,” Rie“,” Cría“,” Atd “,” reune “or” púa”.