PHONETICS AND PHONOLOGY
Segmental Aspects

British English diphthongs: eɪ aɪ ͻɪ əʊ aʊ ɪə eə ʊə

American English diphthongs: eɪ aɪ ͻɪ oʊ aʊ jʊ

Slovak diphthongs: ĭa ĭe ĭu ŭo

The smallest segments of speech are vowels and consonants. All vowels, it means monophthongs, diphthongs and triphthongs, share the same characteristic features defined from the point of view of phonetics and phonology.

From the phonetic point of view, when pronouncing vowels, the airstream passes from the larynx to the lips unobstructed. Diphthongs are complex monosyllabic speech sounds, glides, beginning with one vowel sound and moving to another vowel within the same syllable rapidly and without interruption. If two vowels follow one another in a vowel-group (vowel cluster) and each of them is pronounced in a different syllable, these vowels form a hiatus, not a diphthong. Compare, for instance, the Slovak words dieťa and diéta. While the word dieťa includes two syllables, die-ťa, the word diéta comprises three syllables di-é-ta. There is a syllable boundary between the two vowels in the word di-éta, so this word includes a hiatus, not a diphthong. Other examples for a hiatus are, for example, re-alize, the-atre, do-ing, pi-onier, na-opak, vi-de-o. The Slovak word pionier comprises both a hiatus consisting of i + o, and a diphthong ĭe.

From the phonological point of view, diphthongs function as distinctive sound units which form the centre of syllables, it means one syllable nucleus (peak of sonority).

All diphthongs in both English and Slovak are voiced (the vocal folds are active) and oral (the soft palate is raised), they are defined as sonorants and tones. English diphthongs as well as Slovak diphthongs last approximately twice as long as short vowels. Diphthong quantity in English words is influenced by their position in syllables – if diphthongs are followed by voiceless consonants in syllables, their length is reduced.