Diphthongs contrast with monophthongs.
 Semivowels and approximants are not equivalent in all treatments, and in the English and Italian languages, among others, many phoneticians do not consider rising combinations to be diphthongs, but rather sequences of approximant and vowel
 As a result of their origin (diphthongization of mid vowels under stress), the two true diphthongs appear only in stressed syllables and make morphological alternations with the mid vowels /e/ and /o/

