Timing and placement

stress-timed language; that is, stressed syllables appear at a roughly constant rate, and non-stressed syllables are shortened to accommodate this. Other languages have syllable timing (e.g. Spanish) or mora timing (e.g. Japanese), where syllables or morae are spoken at a roughly constant rate regardless of stress.

Some languages have fixed stress. That is, stress is placed always on a given syllable, as in Finnish and Hungarian (stress always on the first syllable) or Quechua and Polish (stress always on the penult: one syllable before the last) or on third syllable counting backwards (the antepenult), as in Macedonian (see: Stress in Macedonian language). Other languages have stress placed on different syllables but in a predictable way, as in Latin (where stress is conditioned by the structure of the penultimate syllable). They are said to have a regular stress rule.

French words are sometimes said to be stressed on the final syllable, but actually French has no word stress at all. Rather, it has a prosody whereby the final or next-to-final syllable of a string of words is stressed. This string may be equivalent to a clause or a phrase. However, when a word is said alone, it receives the full prosody and therefore the stress as well.

There are also languages like English, Italian and Spanish, where stress is (at least partly) unpredictable. Rather, it is lexical: it comes as part of the word and must be memorized, although orthography can make stress unambiguous for a reader, as is the case in Spanish and Portuguese. In such languages, otherwise homophonous words may differ only by the position of the stress, and therefore it is possible to use stress as a grammatical device.

English does this to some extent with noun-verb pairs such as a récord vs. to recórd, where the verb is stressed on the last syllable and the related noun is stressed on the first; record also hyphenates differently: a réc-ord vs. to re-córd. The German language does this with certain prefixes - for example úm-schrei-ben (to rewrite) vs. um-schréi-ben (to paraphrase, outline) - and in Russian this phenomenon often occurs with different cases of certain nouns (земли́/zemli (genitive case of the Earth, land or soil) and зе́мли (soils or lands - plural form)).

It is common for dialects to differ in their stress placement, as in British English and American English.

[edit] Historical effects of stress

It is common for stressed and unstressed syllables to behave differently as a language evolves. For example, in the Romance languages, the original Latin short vowels /e/ and /o/ have generally become diphthongs when stressed. Since stress takes part in verb conjugation, this has produced verbs with vowel alternation in the Romance languages. For example, the Spanish verb volver has the form volví in the past but vuelvo in the present (see Spanish irregular verbs). Italian shows the same phenomenon, but with /o/ alternating with /uo/ instead. This behaviour is not confined to verbs; for example, Spanish viento "wind" vs. ventilación "ventilation", from Latin ventum.