Stress, rhythm and intonation

English is a strongly stressed language, in which stress is said to be phonemic, i.e. capable of distinguishing words (such as the noun increase, stressed on the first syllable, and the verb increase, stressed on the second syllable). In almost any word of more than one syllable there will be one syllable identified as taking the primary stress, and possibly another taking a secondary stress, as in civilization /ˌsɪvəlaɪˈzeɪʃn̩/, in which the first syllable carries secondary stress, the fourth syllable carries primary stress, and the other syllables are unstressed.

Closely related to stress in English is the process of vowel reduction; for example, in the noun contract the first syllable is stressed and contains the vowel /ɒ/ (in RP), whereas in the verb contract the first syllable is unstressed and its vowel is reduced to /ə/ (schwa). The same process applies to certain common function words like of, which are pronounced with different vowels depending on whether or not they are stressed within the sentence.
English also has strong prosodic stress – the placing of additional emphasis within a sentence on the words to which a speaker wishes to draw attention, and corresponding weaker pronunciation of less important words. As regards rhythm, English is classed as a stress-timed language – one in which there is a tendency for the time intervals between stressed syllables to become equal, with corresponding faster pronunciation of groups of unstressed syllables.

As concerns intonation, the pitch of the voice is used syntactically in English; for example, to convey surprise or irony, or to change a statement into a question. Most dialects of English use falling pitch for definite statements, and rising pitch to express uncertainty, as in questions (particularly yes-no questions). There is also a characteristic change of pitch on strongly stressed syllables, particularly on the "nuclear" (most strongly stressed) syllable in a sentence or intonation group.