2.6 Phonetic features and natural classes

　 In 2.3 it is mentioned that segments are units of phonetic transcription. When we describe each segment in terms of places of articulation, manners of articulation, voicing, position of the tongue, height of the tongue, lip-rounding and tensity, etc., we actually analyze speech sounds into their composing elements, or phonetic features. [] possesses the features [+voiced] [+velar] [+stop]. There are other segments that possess one of the three features, but none that possesses all three. [] has the features [+high] [+back] [+round] [+tense], [] is [-tense] although it shares the rest.

　 Classes of sounds that share a feature or features are called natural classes. The set [] [] [] [] belong to the class [+voiced], while [] [] [] [] voiceless. The feature [+high] specifies the class of vowels [] [] [] [], and the features [-high] [-low] define the class [] [] [] []. The feature[+front] specifies [] [] [] [], and the features [-front] [-back] define [] [] []. The feature [+round] is shared by [] [] [] [].

　 Features form a hierarchy. Some features specify a small class. For example, [+liquid] specifies only two segments. Other features specify a large class. [+anterior], for example, defines labials, labiodentals, interdentals and alveolars, namely, [] [] [] [] [] [][] [] [] [] [] []. [+continuant] specifies all the fricatives, liquids, glides. [+sibilant] (also called [+strident]) is a feature found in [] [] [] [] [] [].

　 Major class features can specify segments across the consonant-vowel boundary. [+syllabic] is a feature that represents all the vowels and [] [] [], as in orgasm, nation, bottle, of which the final syllable may lack a vowel. [+sonorant] is also a major class feature. It is shared by all the vowels, nasals, liquids and glides.

　 Classification of segments by features is the basis on which variations of sounds can be analyzed. This will be discussed in Chapter 3.