Phonetics – the study of the sounds of languages from three basic points of view.
Phonetics studies speech sounds according to their production in the vocal organs (articulatory phonetics), their physical properties (acoustic phonetics), or their effect on the ear (auditory phonetics). All phonetics are interrelated, since human articulatory and auditory mechanisms correspond to each other and are mediated by wavelength, pitch, and the other physical properties of sound. Systems of phonetic writing are aimed at the accurate transcription of any sequence of speech sounds; the best known is the International Phonetic Alphabet. Narrow transcription specifies as many features of a sound as can be symbolized, while broad transcription specifies only as many features of a sound as are necessary to distinguish it from other sounds.
Each language uses a limited number of the humanly possible sounds grouped into phonemes, and the hearer-speaker is trained from childhood to classify them into these groups, rejecting as nonsignificant all sorts of features actually phonetically present. So the English speaker does not notice that he always makes a puff of air when he pronounces the p of pin and never makes the puff with the p of spin; for him they are the same sound. Yet in some languages (as in Sanskrit) just the presence or absence of that puff in both words would indicate a phonemic difference, and two words might differ in meaning because of the puff. In English the two sounds are considered variations of a single sound, the phoneme p, and as such are allophones. In the other situation, aspirated p (p with a puff) and unaspirated p are not allophones but separate phonemes.
Phonemes include all significant differences of sound, including features of voicing, place and manner of articulation, accent, and secondary features of nasalization, glottalization, labialization, and the like. Whereas phonetics refers to the study of the production, perception, and physical nature of speech sounds, phonology refers to the study of how such sounds are combined in particular languages and of how they are used to convey meaning. Systematic sound change through time is treated by comparative and historical linguistics. See grammar; language; writing.