In linguistics, stress is the relative emphasis that may be given to certain syllables in a word, or to certain words in a phrase or sentence. Stress is typically signaled by such properties as increased loudness and vowel length, full articulation of the vowel, and changes in pitch. The terms stress and accent are often used synonymously, but they are sometimes distinguished, with certain specific kinds of prominence (such as pitch accent, variously defined) being considered to fall under accent but not under stress. In this case, stress specifically may be called stress accent or dynamic accent.
The stress placed on syllables within words is called word stress or lexical stress. Some languages have fixed stress, meaning that the stress on virtually any multisyllable word falls on a particular syllable, such as the first or the penultimate. Other languages, like English, have variable stress, where the position of stress in a word is not predictable in that way. Sometimes more than one level of stress, such as primary stress and secondary stress, may be identified. However, some languages are considered to lack lexical stress entirely.
The stress placed on words within sentences is called sentence stress or prosodic stress. This is one of the three components of prosody, along with rhythm and intonation. It includes phrasal stress (the default emphasis of certain words within phrases or clauses), and contrastive stress (used to highlight an item − a word, or occasionally just part of a word − that is given particular focus).
There are various ways in which stress manifests itself in the speech stream, and these depend to some extent on which language is being spoken. Stressed syllables are often louder than non-stressed syllables, and may have a higher or lower pitch. They may also sometimes be pronounced longer. There are sometimes differences in place or manner of articulation – in particular, vowels in unstressed syllables may have a more central (or "neutral") articulation, while those in stressed syllables have a more peripheral articulation. Stress may be realized to varying degrees on different words in a sentence; sometimes the difference between the acoustic signals of stressed and unstressed syllables are minimal.
These particular distinguishing features of stress, or types of prominence in which particular features are dominant, are sometimes referred to as particular types of accent – dynamic accent in the case of loudness, pitch accent in the case of pitch (although this term usually has more specialized meanings), quantitative accent in the case of length, and qualitative accent in the case of differences in articulation. These can be compared to the various types of accent in music theory. In some contexts, the term stress or stress accent is used to mean specifically dynamic accent (or as an antonym to pitch accent in its various meanings).
In Mandarin Chinese, which is a tone language, stressed syllables have been found to have tones realized with a relatively large swing in fundamental frequency, while unstressed syllables typically have smaller swings. (See also Stress in Standard Chinese.)
Stressed syllables are often perceived as being more forceful than non-stressed syllables. Research has shown, however, that although dynamic accent is accompanied by greater respiratory force, it does not mean a more forceful articulation in the vocal tract.
(Much literature emphasizes the importance of pitch changes and pitch motions on stressed syllables, but experimental support for this idea is weak. Nevertheless, most experiments do not directly address the pitch of speech, which is a subjective perceived quantity. Experiments typically measure the speech fundamental frequency, which is objectively measurable, and strongly correlated with pitch, but not quite the same thing.)
Lexical stress, or word stress, is the stress placed on a given syllable in a word. The position of lexical stress in a word may depend on certain general rules applicable in the language or dialect in question, although in some languages it is largely unpredictable, needing to be "learned" for each individual word.
Languages in which the position of the stress can usually be predicted by a simple rule are said to have fixed stress. For example, in Czech, Finnish, Icelandic and Hungarian the stress almost always comes on the first syllable of a word; in Quechua and Polish the stress is almost always on the penultimate syllable; while in Macedonian it comes on the antepenult (third syllable from the end). Other languages have stress placed on different syllables but in a predictable way, as in Classical Arabic and Latin (where stress is conditioned by the structure of the penultimate syllable). They are said to have a regular stress rule.
Statements about the position of stress are sometimes affected by the fact that when a word is spoken in isolation, prosodic factors (see below) come into play, which do not apply when the word is spoken normally within a sentence. French words are sometimes said to be stressed on the final syllable, but this can be attributed to the prosodic stress that is placed on the final syllable (or, if that is a schwa, the next-to-final syllable) of any string of words in that language, and hence also on the last syllable of a word analyzed in isolation. The situation is similar in Mandarin Chinese; see Stress in Standard Chinese. French (and according to some authors, Chinese) can in fact be considered to have no lexical stress.
Languages in which the position of stress in a word is less predictable are said to have variable stress. This applies to English and Russian, and to some extent to Italian and Spanish. Here stress is truly lexical: it must be memorized as part of the pronunciation of an individual word. In such languages stress may be phonemic, in that it can serve to distinguish otherwise identical words; for example, the English words insight and incite are distinguished in pronunciation only by the fact that the stress falls on the first syllable in the former and on the second syllable in the latter. Other examples include umschreiben ("rewrite") vs. umschreiben ("paraphrase, outline") in German, земли́ (genitive of "earth, land") vs. зе́мли (plural of "earth, land") in Russian, ancora ("anchor") and ancora ("more, still, yet") in Italian. English compound nouns can change their meaning based on stress, as with paper bág (a bag made of paper) and páper bag (a bag for carrying newspapers).
Stress placement for some words may differ between dialects. For example, in British English the word labóratory is pronounced with primary stress on the second syllable, while American English stresses the first syllable, láboratory.
Levels of stress
Some languages are described as having both primary stress and secondary stress. A syllable with secondary stress is stressed relative to unstressed syllables, but not as strongly as a syllable with primary stress. As with primary stress, the position of secondary stress may be more or less predictable depending on language. In English it is not fully predictable; for example, the words organization and accumulation both have primary stress on the fourth syllable, but the secondary stress comes on the first syllable in the former word and on the second syllable in the latter. 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 these treatments often disagree with each other.
Peter Ladefoged and other phoneticians have noted that it is possible to describe English with only one degree of stress, as long as unstressed syllables are phonemically distinguished for vowel reduction. They believe that the multiple levels posited for English, whether primary–secondary or primary–secondary–tertiary, are mere phonetic detail and not true phonemic stress, and that often the alleged secondary stress is not characterized by the increase in respiratory activity normally associated with primary stress in English or with all stress in other languages. (For further detail see Stress and vowel reduction in English.)
Prosodic stress, or sentence stress, refers to stress patterns that apply at a higher level than the individual word – namely within a prosodic unit. It may involve a certain natural stress pattern characteristic of a given language, but may also involve the placing of emphasis on particular words because of their relative importance (contrastive stress).
An example of a natural prosodic stress pattern is that described for French above; stress is placed on the final syllable of a string of words (or if that is a schwa, the next-to-final syllable). A similar pattern has been claimed for English (see Levels of stress above): the traditional distinction between (lexical) primary and secondary stress is replaced partly by a prosodic rule stating that the final stressed syllable in a phrase is given additional stress. (A word spoken alone becomes such a phrase, hence such prosodic stress may appear to be lexical if the pronunciation of words is analyzed in a standalone context rather than within phrases.)
Another type of prosodic stress pattern is quantity sensitivity – in some languages additional stress tends to be placed on syllables that are longer (moraically heavy).
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. (Somebody else did.)
I didn't take the test yesterday. (I did not take it.)
I didn't take the test yesterday. (I did something else with it.)
I didn't take the test yesterday. (I took a different one.)
I didn't take the test yesterday. (I took something else.)
I didn't take the test yesterday. (I took it some other day.)
In English, stress is most dramatically realized on focused or accented words. For instance, consider the dialogue
- "Is it brunch tomorrow?"
- "No, it's dinner tomorrow."
In it, the stress-related acoustic differences between the syllables of "tomorrow" would be small compared to the differences between the syllables of "dinner", the emphasized word. In these emphasized words, stressed syllables such as "din" in "dinner" are louder and longer. They may also have a different fundamental frequency, or other properties.
Stress and vowel reduction
In many languages, such as Russian and English, vowel reduction may occur when a vowel changes from a stressed to an unstressed position. In English, unstressed vowels may reduce to schwa-like vowels, though the details vary with dialect (see Stress and vowel reduction in English). The effect may be dependent on lexical stress (for example, the unstressed first syllable of the word photographer contains a schwa, whereas the stressed first syllable of photograph does not), or on prosodic stress (for example, the word of is pronounced with a schwa when it is unstressed within a sentence, but not when it is stressed).
Many other languages, such as Finnish and the mainstream dialects of Spanish, do not have unstressed vowel reduction; in these languages vowels in unstressed syllables have nearly the same quality as those in stressed syllables.
Stress and rhythm
Some languages, such as English, are said to be stress-timed languages; that is, stressed syllables appear at a roughly constant rate, and non-stressed syllables are shortened to accommodate this. This contrasts with languages that have syllable timing (e.g. Spanish) or mora timing (e.g. Japanese), where syllables or moras are spoken at a roughly constant rate regardless of stress. For details, see Isochrony.
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 often 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 tense but vuelvo in the present tense (see Spanish irregular verbs). Italian shows the same phenomenon but with /o/ alternating with /uo/ instead. This behavior is not confined to verbs; note for example Spanish viento "wind" from Latin ventum, or Italian fuoco "fire" from Latin focum.
Spelling and notation for stress
The orthographies of some languages include devices for indicating the position of lexical stress. Some examples are listed below.
- In Modern Greek, all polysyllables are written with an acute accent over the vowel in the stressed syllable. (The acute accent is also used on some monosyllables in order to distinguish homographs, as in η ("the") and ή ("or"); here the stress of the two words is the same.)
- In Spanish orthography, stress may be written explicitly with a single acute accent on a vowel. Stressed antepenultimate syllables are always written with this accent mark, as in árabe. If the last syllable is stressed, the accent mark is used if the word ends in the letters n, s, or a vowel, as in está. If the penultimate syllable is stressed, the accent is used if the word ends in any other letter, as in cárcel. That is, if a word is written without an accent mark, the stress is on the penult if the last letter is a vowel, n, or s, but on the final syllable if the word ends in any other letter. However as in Greek, the acute accent is also used for some words to distinguish various syntactical uses (e.g. té "tea" vs. te a form of the pronoun tú; dónde "where" as a pronoun or wh-complement, donde "where" as an adverb). For more information, see Stress in Spanish.
- In Portuguese, stress is sometimes indicated explicitly with an acute accent (for i, u, and open a, e, o), or circumflex (for close a, e, o). In diphthongs, when marked, the semivowel (or the semivowels) never receives the accent mark. Stress is not marked with diacritics when it can be otherwise predicted from spelling: it is marked only on uncommon pronunciation of pattern of letters.
- In Italian, the graphic accent is needed in words ending with an accented vowel, e.g. città, "city", and in some monosyllabic words which might otherwise be confused with other words, like là ("there") and la ("the"). It may (but by no means must) be written on any vowel when there is a possibility of misunderstanding, for instance condomìni ("condominiums") and condòmini ("joint owners"). See Italian alphabet: Diacritics.
In many languages, various typographical devices (such as italicization) may be used to place emphasis on particular words in written text; see Emphasis (typography). These can function to some extent as equivalents to or ways of representing the prosodic stress used to emphasize words while speaking.
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. Some of these are listed here.
- In the International Phonetic Alphabet (IPA), primary stress is indicated by a high vertical line before the syllable, secondary stress by a low vertical line. Example: [sɪˌlæbəfɪˈkeɪʃən] or /sɪˌlæbəfɪˈkeɪʃən/. Extra stress can be indicated by doubling the symbol: ˈˈ◌.
- Linguists frequently mark primary stress with an acute accent over the vowel, and secondary stress by a grave accent. Example: [sɪlæ̀bəfɪkéɪʃən] or /sɪlæ̀bəfɪkéɪʃən/. This has the advantage that it does not require a decision about syllable boundaries.
- In English dictionaries that show pronunciation by respelling, stress is typically marked with a prime mark placed after the stressed syllable: /si-lab′-ə-fi-kay′-shən/.
- In ad hoc pronunciation guides, stress is often indicated using a combination of bold text and capital letters. Example: si-lab-if-i-KAY-shun or si-LAB-if-i-KAY-shun
- In Russian and Ukrainian dictionaries, stress is indicated with an acute accent (´) on a syllable's vowel (example: вимовля́ння) or, in other editions, an apostrophe just after it (example: гла'сная). Stressing is rare in general texts, but is still used when necessary: compare за́мок (castle) and замо́к (lock).
- In Dutch, ad hoc indication of stress is usually marked by an acute accent on the vowel (or, in the case of a diphthong or double vowel, the first two vowels) of the stressed syllable. Compare achterúítgang (deterioration) and áchteruitgang (back exit).
- Kochanski, G., Shih, C., Jing, H.; Quantitative Measurement of Prosodic Strength in Mandarin, Speech Communication 41(4), November 2003, doi:10.1016/S0167-6393(03)00100-6
- San Duanmu (2000), The Phonology of Standard Chinese, Oxford University Press, p. 134.
- Ladefoged (1975 etc.) A course in phonetics §5.4; (1980) Preliminaries to linguistic phonetics p 83
- M. E. Beckman, Stress and Non-Stress Accent, Dordrecht: Foris (1986) ISBN 90-6765-243-1
- R. Silipo and S. Greenberg, Automatic Transcription of Prosodic Stress for Spontaneous English Discourse, Proceedings of the XIVth International Congress of Phonetic Sciences (ICPhS99), San Francisco, CA, August 1999, pages 2351-2354
- G. Kochanski, E. Grabe, J. Coleman and B. Rosner, Journal of the Acoustical Society of America, volume 118, number 2, pages 1038–1054, doi:10.1121/1.1923349
- Dalʹ, Vladimir Ivanovich (1903). Tolkovyĭ Slovarʹ Zhivogo Velikorusskago I︠a︡zyka. I. A. Boduėna-de-Kurtene (ed.) (3., ispr. i znachitel'no dop. izd ed.). Sankt-Peterburg: Izd. T-va M.O. Vol'f. p. 4.
- Feet and Metrical Stress (The Cambridge Handbook of Phonology)
- Word stress in English The six fundamental rules
-  Word Stress rules based on affixation