The term diphthong It comes from the Latin diphthongus, which in turn has its origin in a word of the Greek language. The term refers to the meeting of a couple of different vowels that are expressed in the same syllable . For example: "song", "dead", "luck".
For the diphthong to exist, one of these vowels (at least) must be weak . In the Spanish language, the weak vowels are the i and the or . The diphthong, therefore, may consist of two different weak vowels ("watch out", "day") or by a strong and a weak vowel (although only in cases where the weak vowel is not tonic, otherwise the diphthong is broken).
If we find ourselves in the presence of a strong and a weak vowel, the diphthong can be growing (when the second vowel constitutes the syllabic nucleus) or decreasing (the syllabic nucleus is in the first vowel).
Examples of increasing diphthong are "stone", and "Easter", while examples of decreasing diphthong are "landscape", "Pseudo" and "Corticosteroid".
In addition to these two kinds of diphthongs, it must be made clear that there is a third modality called homogenous diphthong. In this case it is determined that it is the one that is characterized because it begins and ends with a closed vowel. This results in two possible combinations therefore: iu and ui.
It is important to underline that when we refer to this group of vowels in terms of language, it is inevitable that we also make known other types of union of these letters that, at times, may become confused with that one. Specifically, we are referring to hiatus.
The aforementioned hiatus are the union of two vowels that are pronounced in different syllables and, therefore, do not form a diphthong. More precisely those usually consist of a closed vowel and another strong vowel or two strong ones.
In the first case cited, we would have as examples words such as country, barb, corn, Maria or Raul. As a sample of what a hiatus is composed of two strong vowels we would have the following terms: zoo, saeta, pawn, theater or poet.
Likewise, it must be made clear that when we talk about diphthongs and hiatus, it is inevitable to refer to what triptongs are. These are defined as the union of three vowels in a single syllable, more precisely their formula would be: closed vowel + open vowel + closed vowel. Examples of this are the words criáis, scallop, Mieira, riáis or asociáis.
There are various spelling rules linked to diphthongs. The and , when it appears at the end of the word , it can form diphthong (or even tryptongo) since it has vowel value (it sounds like i ). For example: "Gualeguay". If it is at the beginning of the term, or in the middle and retains its consonant property, it cannot form a vowel grouping ("Beach").
Moreover, the h mute , which does not produce sound, does not prevent the establishment of diphthong even when it is in the middle of two vowels: "evict", "goddaughter".