Since stress can be realised through a wide range of phonetic properties, such as loudness, vowel length, and pitch (which are also used for other linguistic functions), it is difficult to define stress solely phonetically.
There are various ways in which stress manifests itself in the speech stream, and they depend to some extent on which language is being spoken.
A prominent syllable or word is said to be accented or tonic; the latter term does not imply that it carries phonemic tone.
In Mandarin Chinese, which is a tonal language, stressed syllables have been found to have tones that are realized with a relatively large swing in fundamental frequency, and unstressed syllables typically have smaller swings.
For example, in Czech, Finnish, Icelandic, Hungarian and Latvian, the stress almost always comes on the first syllable of a word.
French and Georgian (and, according to some authors, Mandarin Chinese)[6] can be considered to have no real lexical stress.
Stress in these languages is usually truly lexical and must be memorized as part of the pronunciation of an individual word.
Examples from other languages include German Tenor ([ˈteːnoːɐ̯] 'gist of message' vs. [teˈnoːɐ̯] 'tenor voice'); and Italian ancora ([ˈaŋkora] 'anchor' vs. [aŋˈkoːra] 'more, still, yet, again').
There may also be limitations on certain phonemes in the language in which stress determines whether they are allowed to occur in a particular syllable or not.
That is the case with most examples in English and occurs systematically in Russian, such as за́мок ([ˈzamək], 'castle') vs. замо́к ([zɐˈmok], 'lock'); and in Portuguese, such as the triplet sábia ([ˈsaβjɐ], 'wise woman'), sabia ([sɐˈβiɐ], 'knew'), sabiá ([sɐˈβja], 'thrush').
In some analyses, for example the one found in Chomsky and Halle's The Sound Pattern of English, English has been described as having four levels of stress: primary, secondary, tertiary, and quaternary, but the treatments often disagree with one another.
[citation needed] Peter Ladefoged and other phoneticians have noted that it is possible to describe English with only one degree of stress, as long as prosody is recognized and unstressed syllables are phonemically distinguished for vowel reduction.
Prosodic stress is also often used pragmatically to emphasize (focus attention on) particular words or the ideas associated with them.
Doing this can change or clarify the meaning of a sentence; for example: I didn't take the test yesterday.
As in the examples above, stress is normally transcribed as italics in printed text or underlining in handwriting.
In English, stress is most dramatically realized on focused or accented words.
In these emphasized words, stressed syllables such as din in dinner are louder and longer.
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 often become diphthongs when stressed.
[15][16] The idea is that if listeners perform poorly on reproducing the presentation order of series of stimuli that minimally differ in the position of phonetic prominence (e.g. [númi]/[numí]), the language does not have word stress.
[16] The language has generally been described as having contrastive word stress or accent as evidenced by numerous stem and stem–clitic minimal pairs such as /mɒhi/ [mɒ.hí] ('fish') and /mɒh-i/ [mɒ́.hi] ('some month').
The authors argue that the reason why Persian listeners are "stress-deaf" is that their accent locations arise postlexically.
Stress "deafness" has been studied for a number of languages, such as Polish[17] and French learners of Spanish.
[18] The orthographies of some languages include devices for indicating the position of lexical stress.
Some examples are listed below: Though not part of normal orthography, a number of devices exist that are used by linguists and others to indicate the position of stress (and syllabification in some cases) when it is desirable to do so.