Tenseness

In phonology, tenseness is a particular vowel or consonant quality that is phonemically contrastive in many languages, including English. It has also occasionally been used to describe contrasts in consonants. Unlike most distinctive features, the feature [tense] can be interpreted only relatively, that is, in a language like English that contrasts (e.g. beat) and  (e.g. bit), the former can be described as a tense vowel while the latter is a lax vowel. Another example is Vietnamese, where the letters ă and â represent lax vowels, and the letters a and ơ the corresponding tense vowels. Some languages like Spanish are often considered as having only tense vowels, but since the quality of tenseness is not a phonemic feature in this language, it cannot be applied to describe its vowels in any meaningful way.

Comparison between tense and lax vowels
In general, tense vowels are more close (and correspondingly have lower first formants) than their lax counterparts. Tense vowels are sometimes claimed to be articulated with a more advanced tongue root than lax vowels, but this varies, and in some languages it is the lax vowels that are more advanced, or a single language may be inconsistent between front and back or high and mid vowels (Ladefoged and Maddieson 1996, 302–4). The traditional definition, that tense vowels are produced with more "muscular tension" than lax vowels, has not been confirmed by phonetic experiments. Another hypothesis is that lax vowels are more centralized than tense vowels. There are also linguists who believe that there is no phonetic correlation to the tense-lax opposition.

In many Germanic languages, such as RP English, standard German, and Dutch, tense vowels are longer in duration than lax vowels; but in other languages, such as Scots, Scottish English, and Icelandic, there is no such correlation.

Since in Germanic languages, lax vowels generally only occur in closed syllables, they are also called checked vowels, whereas the tense vowels are called free vowels as they can occur at the end of a syllable.

Tenseness in consonants
Occasionally, tenseness has been used to distinguish pairs of contrasting consonants in languages. Korean, for example, has a three-way contrast among stops; the three series are often transcribed as -  -. The contrast between the series and the  series is sometimes said to be a function of tenseness: the former are lax and the latter tense. In this case the definition of "tense" would have to include greater glottal tension.

In some dialects of Irish and Scottish Gaelic, contrasts are found between on the one hand and  on the other hand. Here again the former set have sometimes been described as lax and the latter set as tense. It is not clear what phonetic characteristics other than greater duration would be associated with tenseness in this case.

Some researchers have argued that the contrast in German traditionally described as voicing is in fact better analyzed as tenseness, since the latter set is voiceless in Southern German. German linguistics call the distinction fortis and lenis rather than tense and lax. Tenseness is especially used to explain stop consonants of the Alemannic German dialects because they have two series of them that are identically voiceless and unaspirated. However, it is debated whether the distinction is really a result of different muscular tension, and not of gemination.