Binary Features

Binary features in linguistics are used to classify sounds. They are called binary because they have the feature, or they do not. Sounds with the feature have the + symbol, and sounds without the feature have the - symbol.

All sounds can be divided into voiced and voiceless. Consonants such as /b/ and /g/ are voiced, and /p/ and /k/ are voiceless. The consonants /b/ and /g/ are [+voice], and the sounds /p/ and /k/ are [-voice].

Vowels can be divided into rounded and unrounded. The vowels /e/ and /i/ are unrounded, and the vowels /o/ and /u/ are rounded. The vowels /e/ and /i/ are thus [-round], and the vowels /o/ and /u/ are [+round}.

All vowels are vocalic, and all consonants are consonantal. Semi-vowels such as the first segment of water and the first segment of year are neither vocalic nor consonantal. Though they have properties of both vowels and consonants, they belong to neither category. Here is a comparison:

vowels: [+vocalic] [-consonantal]

consonants [-vocalic] [+consonantal] 

semi-vowels [-vocalic] [-consonantal] 

The consonants /b/ and /m/ are both plosives and they are both bilabial. However, one feature can distinguish the two. The consonant /b/ is [-nasal] and the consonant /m/ is [+nasal].

The vowels /i/ and /I/ are both high front unrounded vowels. One feature can distinguish the two. The vowel /i/ is tense, and the vowel /I/ is lax. With binary features, the vowel /i/ is [+tense] and  the vowel /I/ is [-tense].

Binary features are features that are mutually exclusive. Sounds which are voiced cannot be unvoiced, and sounds which are voiceless cannot be voiced. Binary features are very useful for the classification of speech sounds.