backness

Backness is a basic feature of vowel quality in phonetics and phonology that describes where the tongue lies in the mouth during articulation. It classifies vowels as front, central, or back, with front vowels produced with the tongue pushed toward the front of the mouth and back vowels with the tongue retracted toward the back; central vowels lie between.

In articulation, backness interacts with tongue height and rounding. Examples in standard descriptions include front high vowels like /i/ as in "beat," front mid vowels like /e/ as in "bait," back high vowels like /u/ as in "goose," and back mid vowels such as /ɔ/ in some dialects. Central vowels such as /ə/ occur in many languages. Not all languages have a three-way backness contrast; some distinguish only front vs back, or have more complex inventories. Rounding often correlates with backness—front vowels are typically unrounded, back vowels often rounded, though many languages exhibit exceptions.

Acoustically, backness is associated with the second formant frequency (F2): front vowels have higher F2 values, producing a more fronted quality, while back vowels have lower F2 values. Vowel shifts can move vowels toward more front or more back regions, and vowel inventories vary in how much they emphasize front versus back vowels.

In linguistic analysis, backness is treated as a feature alongside height and rounding. It is essential for distinguishing words and for understanding vowel system typology across languages.