What is a diphthong?

A diphthong is defined as a complex vowel sound that glides from one vowel quality to another within the same syllable. This occurs when the tongue and mouth change position during the articulation of the vowel, resulting in a smooth transition. For instance, in the English language, the vowel sound in the word "coin" transitions from the "o" sound to the "i" sound, creating a single phonetic unit that encompasses both vowel qualities.

Understanding that a diphthong is not simply a single vowel sound helps clarify why it is distinct from the other options. A diphthong involves a combination of vowel sounds that can change the meaning of words, whereas a single vowel sound represents a static position of the tongue and vocal tract. Additionally, while consonants do involve restrictions in airflow, they are categorized differently; thus, these sounds cannot be considered diphthongs. Furthermore, phonetic errors refer to mistakes made in speech production rather than the fluid, intentional sound of a diphthong.