Vocal stress
In linguistics, stress is the emphasis (shown by more forceful, louder, and higher-pitched voice) given to some syllables (usually no more than one in each word). In many languages, long words have a secondary stress a few syllables away from the primary stress.
Some languages have fixed stress, i. e. stress is placed always on a given syllable, as in French (where words are always stressed in the last syllable), Finnish (stress always on the first syllable) or Quechua (always on the penultima -- the syllable before the last one). Other languages have stress placed on different syllables in a predictable way (they're said to have a regular stress rule), such as Latin.
There are also languages like English or Spanish, where stress is unpredictable and arbitrary, being lexical -- it comes as part of the word and must be learned with it. In this kind of language two words can differ only by the position of the stress, and therefore it's possible to use stress as a derivative or inflectional device. English shows this with noun/verb pairs such as to record ("to register, to inscribe") vs. a record ("a register, an entry"), where the verb is stressed on the last syllable and the corresponding noun is stressed on the first.
In Romance languages, stress takes part in the verb conjugation and it produces an interesting phenomenon by which the vowels /e/ and /o/ in the root of some verbs become diphthongs when stressed. For example, in Spanish the verb volver has the forms volví, volviste, volvió in the past, and vuelvo, vuelves, vuelve in the present. In these Spanish verbs, stressed /o/ becomes /ue/ and stressed /e/ becomes /ie/ (Italian has /o/ → /uo/ instead).
There are languages that do not have a stress rule, instead possessing accentual systems based on pitch or tone (i. e. paying attention to the relative height of the syllable, instead of its loudness). I question the accuracy of this. In English, stressed syllables have higher pitch than unstressed ones. In tone languages, the tone can rise or fall during articulation of the syllable, rather than some syllables, the stressed one, having higher pitch than the others.
Stress in poetry
Poetry in English depends upon stress to establish the meter of the poem. Stress is usually thought of as strong or weak. Some people distinguish a third, intermediate stress level.
For example: in the word reconsider, the stress pattern is 'recon'sider (intermediate - weak - strong - weak).
See also
