Weak vowels
Among unstressed syllables it is useful to distinguish between those that nevertheless contain a strong vowel and those that have a weak vowel. This distinction has implication for syllabification and for rhythm.
A stressed syllable must always contain a strong vowel. All the syllables in the following words, whether stressed or unstressed, are strong-vowelled: red, hope, bedtime, undone, acorn.
The vowels ә, i, u, are always weak. The vowel ɪ too is weak in many cases, and sometimes ʊ in BrE and oʊ in AmE. The unstressed syllables in the following words are al weak-vowelled: allow, happy, situation, remember, standard, stimulus. The weak vowel ә may be realized in the form of a syllabic consonant, as in suddenly. If a diphthong is created through the compression of weak syllables, it remains weak, as in annual.
The distinction between weak ɪ and ә has the power of distinguishing words in RP. The words rabbit and abbot do not rhyme. In certain other kinds of English this distinction may be neutralized, with ә used instead of weak ɪ in virtually all positions, or with the choice between ɪ and ә dependent upon the phonetic context.
Even in RP and other kinds of English that maintain the distinction between weak ɪ and ә, many words may be heard with either pronunciation, and this is shown in LPD. For example, carelessness, civil, private.
Y Spelling-to-sound
At the beginning of a word or syllable, where the spelling is y, the pronunciation is j, as in yet, beyond.
Elsewhere, the same pronunciation correspond to y as to i, namely
ɪ (short) as in crystal
aɪ (long) as in type
or y may be part of one of the digraphs ay, ey, oy, uy.
The sound j is also sometimes written i, as in onion. It frequently arises through compression of i with a following weak vowel, as in convenient.
As part of the sequence juː, it is regularly written eu, ew, u, ue.
Z Spelling-to-sound
Where the spelling is z, the pronunciation is regularly z, as in lazy.
Where the spelling is double zz, the pronunciation is again z, as in dazzle.
Because of yod coalescence, the pronunciation is occasionally ʒ, as in seizure.
In certain words borrowed from foreign languages, spelling with z, zz or the foreign digraph tz, the pronunciation is ts, as in Nazi, pizza, quarts.
The sound z is also regularly written s, as in choose.