We know that the phonic medium can be studied from four points of view: the articulatory, the acoustic, the auditory, and the functional.
We may consider the branches of phonetics according to these aspects. Articulatory phonetics is the study of the way the vocal organs are used to produce speech sounds. Acoustic phonetics is the study of the physical properties of speech sounds. Auditory phonetics is the study of the way people perceive speech sounds. Of these three branches of phonetics, the longest established, and until recently the most highly developed, is articulatory phonetics. For this reason, most of terms used by linguists to refer to speech-sounds are articulatory in origin.
Phoneticians are also interested in the way in which sound phenomena function in a particular language. In other words, they study the abstract side of the sounds of language. The branch of phonetics concerned with the study of the functional (linguistic) aspect of speech sounds is called phonology. By contrast with phonetics, which studies all possible sounds that the human vocal apparatus can make, phonology studies only those contrasts in sound which make differences of meaning within language.
Besides the four branches of phonetics described above, there are other divisions of the science. We may speak of general phonetics and the phonetics of a particular language (special or descriptive phonetics). General phonetics studies all the sound-producing possibilities of the human speech apparatus and the ways they are used for purpose of communication. The phonetics of a particular language studies the contemporary phonetic system of the particular language, i.e. the system of its pronunciation, and gives a description of all the phonetic units of the language. Descriptive phonetics is based on general phonetics.
Linguists distinguish also historical phonetics whose aim is to trace and establish the successive changes in the phonetic system of a given language (or a language family) at different stages of its development. Historical phonetics is a part of the history of language.
Closely connected with historical phonetics is comparative phonetics whose aims are to study the correlation between the phonetic systems of two or more languages and find out the correspondences between the speech sounds of kindred languages.
Phonetics can also be theoretical and practical. At the faculties of Foreign Languages in this country, two courses are introduced:
1. Practical, or normative, phonetics that studies the substance, the material form of phonetic phenomena in relation to meaning.
2. Theoretical phonetics, which is mainly concerned with the functioning of phonetic units in language.
This dichotomy is that which holds between theoretical and applied linguists. Briefly, theoretical linguistics studies language with a view to constructing theory of its structure and functions and without regard to any practical applications that the investigation of language might have. Applied linguistics has as its concerns the application of the concepts and findings of linguistics to a variety of practical tasks, including language teaching.
All the branches of phonetics are closely connected not only with one another but also with other branches of linguistics. This connection is determined by the fact that language is a system whose components are inseparably connected with one another.
Phonetics is also connected with many other sciences. Acoustic phonetics is connected with physics and mathematics. Articulatory phonetics is connected with physiology, anatomy, and anthropology. Historical phonetics is connected with general history of the people whose language is studied; it is also connected with archaeology. Phonology is connected with communication (information) theory, mathematics, and statistics.