the use of changes in pitch to indicate the difference between statements and questions). Personal characteristics are not linguistically significant. It is not possible to say with any accuracy which aspects of prosody are found in all languages and which are specific to a particular language or dialect. Intonation Some writers (e.g., O'Connor and Arnold) have described intonation entirely in terms of pitch, while others (e.g., Crystal) propose that what is referred to as "intonation" is, in fact, an amalgam of several prosodic variables. The form of English intonation is often said to be based on three aspects: The division of speech into units The highlighting of particular words and syllables The choice of pitch movement (e.g., fall or rise) These are sometimes known as tonality, tonicity and tone (and collectively as "the three T's"). An additional pitch-related variation is pitch range; speakers are capable of speaking with a wide range of pitch (this is usually associated with excitement), while at other times with a narrow range. English has been said to make use of changes in key; shifting one's intonation into the higher or lower part of one's pitch range is believed to be meaningful in certain contexts. Stress From the perceptual point of view, stress functions as the means of making a syllable prominent; stress may be studied in relation to individual words (named "word stress" or lexical stress) or in relation to larger units of speech (traditionally referred to as "sentence stress" but more appropriately named "prosodic stress"). Stressed syllables are made prominent by several variables, by themselves or in combination. Stress is typically associated with the following: pitch prominence, that is, a pitch level that is different from that of neighbouring syllables, or a pitch movement increased length (duration) increased loudness (dynamics) differences in timbre: in English and some other languages, stress is associated with aspects of vowel quality (whose acoustic correlate is the formant frequencies or spectrum of the vowel). Unstressed vowels tend to be centralized relative to stressed vowels, which are normally more peripheral in quality These cues to stress are not equally powerful. Cruttenden, for example, writes "Perceptual experiments have clearly shown that, in English at any rate, the three features (pitch, length and loudness) form a scale of importance in bringing syllables into prominence, pitch being the most efficacious, and loudness the least so". When pitch prominence is the major factor, the