So far, we have mainly been looking at features concerning individual sounds or phonemes. If we investigate phonetic or phonological detail in this way, we are working on the segmental level since each phoneme is usually assumed to be one segment of speech. Once we move on to look at larger chunks of speech that span a number of segments, such as whole words or phrases, etc., we are dealing with features on the suprasegmental level. As suprasegmental phonetics & phonology represent fairly complex areas of research, we can only explore them very superficially here by taking a brief look at the two phenomena of word stress and intonation.
In polysyllabic words, one or more syllables tend to have a higher emphasis on them than others. This penomenon is known as word stress, as opposed to emphasising particular words within a larger unit, such as a clause, which is usually referred to as sentence stress. Word stress can sometimes be used distinctively, e.g. in distinguishing between homograph verbs and nouns, such as /ˈpɜ:mɪt/ and /pəˈmɪt/. Most systems usually at least distinguish between three levels of stress, primary (indicated by ˈ), secondary (indicated by ˌ) and unstressed, but a few also include a tertiary level.
Think of some further examples of words that may be distinguished through their stress patterns.
In intonation, the frequency of vibration of the vocal folds is modulated in order to achieve particular effects on the speaker. These effects may be attitudinal, in that e.g. a relatively level intonation may convey boredom, or serve to distinguish between syntactic units of declarative/imperative vs. interrogative nature. In the latter case, the ‘declarative’ types are often assumed to be signalled by a falling intonation contour, whereas a rising contour is said to convey an interrogative character, although this is certainly not true for all accents of English. A further function of intonation is to convey incompleteness (rising or level tone), e.g. in lists, as opposed to finality (falling tone), which can be used as structuring devices.
For further information on word stress, see the Stress & Prominence page, and for intonation, the Intonation page of my Phonetics & Phonology course.