back vowel, and sounds quite different from an English endolabial . Swedish and Norwegian are the only two known languages in which the feature is contrastive; they have both exo- and endo-labial close front vowels and close central vowels, respectively. In many phonetic treatments, both are considered types of rounding, but some phoneticians do not believe that these are subsets of a single phenomenon and posit instead three independent features of rounded (endolabial), compressed (exolabial), and unrounded. The lip position of unrounded vowels may also be classified separately as spread and neutral (neither rounded nor spread). Others distinguish compressed rounded vowels, in which the corners of the mouth are drawn together, from compressed unrounded vowels, in which the lips are compressed but the corners remain apart as in spread vowels. Front, raised and retracted The conception of the tongue moving in two directions, high–low and front–back, is not supported by articulatory evidence and does not clarify how articulation affects vowel quality. Vowels may instead be characterized by the three directions of movement of the tongue from its neutral position: front (forward), raised (upward and back), and retracted (downward and back). Front vowels ( and, to a lesser extent , etc.), can be secondarily qualified as close or open, as in the traditional conception, but this refers to jaw rather than tongue position. In addition, rather than there being a unitary category of back vowels, the regrouping posits raised vowels, where the body of the tongue approaches the velum (], etc.), and retracted vowels, where the root of the tongue approaches the pharynx (, etc.): front raised retracted Membership in these categories is scalar, with the mid-central vowels being marginal to any category. Nasalization Nasalization occurs when air escapes through the nose. Vowels are often nasalised under the influence of neighbouring nasal consonants, as in English hand . Nasalised vowels, however, should not be confused with nasal vowels. The latter refers to vowels that are distinct from their oral counterparts, as in French vs. . In nasal vowels, the velum is lowered, and some air travels through the nasal cavity as well as the mouth. An oral vowel is a vowel in which all air escapes through the mouth. Polish and Portuguese also contrast nasal and oral vowels. Phonation Voicing describes whether the vocal cords are vibrating during the articulation of a vowel. Most languages have only voiced vowels, but several