The phonetics of stressed syllables
As an organization unit, syllables play a role in the overall rhythm and flow of language, especially by having some syllables be stressed, which gives them more prominence in the linguistic signal. In spoken languages, stressed syllables are often articulated with some combination of increased loudness, longer duration, and/or higher pitch. However, languages can vary quite a lot in exactly which phonetic properties are used for stressed syllables.
Degrees of stress
In spoken languages, words can easily have many syllables, such as the English word internationalization, which has eight syllables, or the German word Kraftfahrzeughaftpflichtversicherung ‘motor vehicle indemnity insurance’, which has nine syllables. Even with just three or four syllables, there is room for multiple degrees of stress within a single word. In most spoken languages, usually there is exactly one syllable per word with the highest degree of stress, which is called primary stress and is marked in the IPA with an upper tick mark [ ˈ ] before the onset of the syllable with primary stress.
All other stressed syllables can be said to have secondary stress, which is marked in the IPA with a lower tick mark [ ˌ ] before the onset of the stressed syllable (note that this diacritic is distinct from the syllabic diacritic [ˌ] which always goes under a symbol; the secondary stress mark [ˌ] always goes before a symbol). The remaining syllables are unstressed, which has no dedicated IPA symbol.
We can see all three levels of stress in the word [ˈbʌ.niˌhʌɡ] bunny hug, which is used in Saskatchewan English to refer to a hoodie. Note that the stress marks are used as syllable boundaries, so no [.] is needed to mark a syllable boundary in a position where [ˈ] or [ˌ] are used. However, some linguists will still mark the syllable boundary separately, so you may sometimes see transcriptions like [ˈbʌ.ni.ˌhʌɡ] instead of [ˈbʌ.niˌhʌɡ].
Stress is commonly marked instead with non-IPA diacritics, with accent marks over the nucleus (or over σ when discussing stress patterns across syllables generally): the acute accent [ ˊ ] for primary and the grave accent [ ˋ ] for secondary, and sometimes also the breve accent [ ˘ ] for unstressed, if it needs to be explicitly marked. Using this system, bunny hug could be transcribed as [bʌ́nihʌ̀ɡ] or [bʌ́nĭhʌ̀ɡ]. However, since these diacritics have other uses in the IPA (see Section 3.7 for the use of [ˊ] and [ˋ] as tone diacritics), they must be used carefully to avoid ambiguity.
Lexical versus predictable stress
Many spoken languages have lexical stress, which means that the placement of stress is mostly unpredictable and must be memorized for each word. This can create minimal pairs, such as [ˈtɑɾu] ‘fast runner’ versus [tɑˈɾu] ‘batter’ and [ˈbɛɫu] ‘basket’ versus [bɛˈɫu] ‘flute’ in Khowar, a Dardic language of the Indo-European family, spoken in Pakistan.
In other spoken languages, stress is fully predictable based on the structure of the syllables in a word, so that two words with the same syllable structures but different phones would always have the same stress pattern. In such languages, the rules governing stress assignment can be quite complicated, and a full analysis is beyond the scope of this textbook. However, there are a few broad patterns for predictable stress in spoken languages.
First, although most words usually have one and only one primary stress, short function words like prepositions or conjunctions might be unstressed within a sentence or larger conversation, as in I’m going to the store to buy milk and eggs, where the preposition to and the conjunction and are usually unstressed. In contrast, some complex words might have multiple syllables with roughly equal primary stress, as in [ˈklinˈʃeɪvn̩] clean-shaven, which sounds a bit odd if you try to use secondary stress on one of the first two syllables.
Second, primary stress is nearly always on one of the first two or the last two syllables in a word. Stress on the first syllable is called initial stress, stress on the second syllable is called peninitial stress, stress on the final syllable is called ultimate stress, and stress on the second syllable from the end is called penultimate stress. In some languages, primary stress may be antepenultimate, on the third syllable from the end, allowing the final syllable to be invisible to stress, as if it were not there. Interestingly, we do not seem to find the equivalent of third stress from the beginning, likely because the first syllable is very psychologically prominent, and so it cannot be ignored in the same way the final syllable can be.
Finally, secondary stress in longer words often occurs in a regular rhythm, skipping every other syllable, so that stressed and unstressed syllables generally alternate with each other. However, there is a great deal of complexity across the world’s spoken languages in how secondary stress is assigned.
But despite all the complexity, there are still some consistent generalizations. We do not seem to find spoken languages that consistently have primary stress on, say, the middle syllable of every word or the fifth syllable of every long word, nor do we find languages that consistently alternate two stressed syllables with two unstressed syllables throughout every word. This suggests that there are deeper underlying principles that govern how stress is assigned, perhaps relating to the purpose of stress.
For example, stress might help with processing of the linguistic signal, so it should be relatively regular (to be more easily recognizable) and anchored to the boundaries of words (which are otherwise hard to determine in ordinary conversation). In other words, not all imaginable stress patterns are possible. Instead, there seems to be a small set of very specific restrictions on how stress works.
Stress-timed and syllable-timed languages
Languages fall into two major categories based on their rhythm: stress-timed and syllable-timed languages.
Stress-timed languages are characterized by the tendency for stressed syllables to occur at roughly equal intervals, regardless of how many syllables are between them. This often requires unstressed syllables to be reduced in order to prioritize stressed syllables. For example, in the sentence The old woman lost her pair of scissors the stressed syllables (underlined) fall at regular intervals, even though the number of syllables between them varies. English and German are classic examples of stress-timed languages.
In contrast, syllable-timed languages are characterized by every syllable occurring at roughly equal intervals, regardless of whether it is stressed or unstressed. As each syllable takes roughly the same amount of time to pronounce, these languages are perceived as having an even flow. Languages like Spanish and Turkish are classic examples of syllable-timed languages.
CC-BY-NC-SA 4.0, adapted from Catherine Anderson, Bronwyn Bjorkman, Derek Denis, Julianne Doner, Margaret Grant, Nathan Sanders, and Ai Taniguchi, Essentials of Linguistics. 2nd ed. with edits by Elif Kara and Anatol Stefanowitsch; additions on stress-timing and syllable timing by Kirsten Middeke.