Vowel features describe the height of the tongue in the oral cavity (high, mid, low), the part of the tongue (front, central, back), the degree of tension in the tongue and lips (tense/lax), which is sometimes correlated with the position of the root of the tongue (advanced tongue root – ATR) and (retracted tongue root – RTR), and the position of the lips (+/- round).
- high: the tongue is raised towards the hard or soft palate
- low: the tongue is lowered away from the hard or soft palate
- front: the blade of the tongue
- back: the body of the tongue or dorsum
Beyond a very introductory level, binary features are preferred when describing vowels, thus avoiding the usage of the terms ‘mid’ and ‘central’, except where specific languages require very detailed account.
Vowels are labeled as following:
high [+high] front [-back] mid [-high, -low] central and back [+back] low [+low]
A binary classification is also possible when there are more than two distinctions, one of which is more salient. Vowel height can be categorized by [-/+low] since high and low vowels are more common in most languages than mid. Thus high and mid are classified as [-low].
When describing a vowel, list the features in these orders.
- part of the tongue
/a/ – [low, +back, lax, -round] /u/ – [+high, +back, tense, +round]
These terms are often used interchangeably with Advanced and Retracted Tongue Root (ATR/RTR), however this distinction involves more than simply the root of the tongue. Tenseness can be more generally distributed throughout the oral cavity as well as in a greater area of the tongue.
ATR/RTR (advanced and retracted tongue root) – when the base of the tongue is forward, lowering the larynx, or retracting the base of the tongue
Other features of vowels in Standard American English include:
- nasal: vowels that precede nasal consonants, e.g., [sĩn] ‘seen’
- devoiced: vowels found flanked by voiceless obstruents, e.g., [th ḁp] ‘top’
- long: vowel that precede voiced phonemes are slightly lengthened in contrast to those that precede voiceless sounds, e.g., [sit] ‘seat’ vs. [si:d] ‘seed’