Unlike most distinctive features, the feature [ tense ] can be interpreted only relatively, often with a perception of greater tension or pressure in the mouth, which, in a language like English, contrasts between two corresponding vowel types : a "'tense vowel "'and a "'lax vowel " '.
22.
The terms " checked vowel " and " free vowel " correspond closely to the terms " lax vowel " and " tense vowel " respectively, but many linguists prefer to use the terms " checked " and " free ", as there is no clearcut phonetic definition of vowel tenseness and because by most attempted definitions of tenseness and are considered lax even though they behave in American English as free vowels.
