Question. Tell me, what is odd in this as an example of an English sentence? Answer. Unlike this one, it contains no diphthongs, only pure vowels (if itΓÇÖs spoken in standard English). A diphthong is the travelling process from one technically pure vowel to another. The vowel sounds in lad, and don, are pure vowels, those in laid and down are diphthongs. During the speaking of a pure vowel the position of the tongue and mouth stays fixed. A diphthong requires movement.
Try to analyse what happens when you speak the word mate. Extend the vowel as if you were singing it on a long, held note. The vowel sound you make has little to do with the letter a, but travels from something like the e sound in met, through the i in mitt, to the ee in meet. If a composer has set the word mate on just one note, the singer has to decide whether to place two distinct vowels (and where the shift should come) or to let the vowel travel from e to ee over the whole time-span of the note. Neither solution is satisfactory for an audience trying to identify the word. Try them out. The first choice transforms the effect of the word into that of met with a strange defect before the final consonant. The second sounds ugly and unnatural.
The best composers will not expose diphthongs to long held notes. One alternative is to set them over two or more notes, allowing the distinct vowels within the diphthong to be placed separately. Diphthongs cause particular problems when set as the final sound of a musical phrase. It is easier to find a way round the problem, however, if they occur in the lower part of the voice. Listen (in the AcademyΓÇÖs Practice Room) to BrittenΓÇÖs setting of and now am full of tears.
