Stress and vowel reduction in English

Stress is a prominent feature of the English language, both at the level of the word (lexical stress) and at the level of the phrase or sentence (prosodic stress). Absence of stress on a syllable, or on a word in some cases, is frequently associated in English with vowel reduction – many such syllables are pronounced with a centralized vowel (schwa) or with certain other vowels that are described as being "reduced" (or sometimes with a syllabic consonant as the syllable nucleus rather than a vowel). Various phonological analyses exist for these phenomena.

For example, in the following sentence, a speaker would typically pronounce have with a schwa, as /həv/ or /əv/ (homophonous with of):

Alice and Bob have arrived.

But in other contexts where the word carries stress, it would be pronounced in its "strong" (unreduced) form as /hæv/ (homophonous with halve). For example:

Alice and Bob have three children.

[In response to the question "Have Alice and Bob arrived?"] They have.