In English, vowels in unstressed syllables are usually reduced.
Reduction is a historical process of weakening, shortening or disappearance of vowel sounds in unstressed positions. This phonetic phenomenon, as well as assimilation, is closely connected with the general development of the language system. Reduction reflects the process of lexical and grammatical changes.
Reduction may be of the following types:
1) qualitative, which is divided into reduction Type A and Type B.
Type A (when the vowels i, e, y are in an unstressed position). Subjecting to this type of reduction these vowels are pronounced [ɪ]
Type B (when the vowels a, o, u are in an unstressed position). Subjecting to this type of reduction these vowels are pronounced [ə]
po 'lite [pə'laɪt]'lyrical ['lɪrɪkəl ]
quantitative. It is shortening of the length of a long vowel sound.
me [ mi˙] he [hi˙]
complete. It is the disappearance of a vowel sound. It occurs when an unstressed vowel occupies the position after the stressed one and it is between a noiseless sound and a sonorant one.
