The Moscow linguists - R.I. Avanesov, A.A. Reformatsky, V.N. Sidorov, P.S.Kuznetsov and others.
The Leningrad school - L.V. Shcherba (the founder of this school), L.R. Zinder, M.I. Matusevitch and others.
One of the main problems of phonological analysis is to establish the inventory of phonemes of a language. Another problem of such analysis deals with cases of neutralization when it is necessary to state the phonemic status of a sound in neutral position (i.e. in words and their grammatical forms in which the phonemes lose their distinctive function due to the neutralization of a phonemic opposition resulting from the loss of a minimal DF by one member of the opposition).
Such problems are solved in a special branch of phonology - morphophonology (or morphonology).
Prof. Vassilyev defines morphonology as the branch of science which "ůstudies the distribution of speech sounds and the relationship between them in different derivatives from the same root or in different grammatical forms of the same word or in different allomorphs of the same morpheme with a view to establish the phonemic status of these morphologically correlated sounds" [Vassilyev 1970: 169].
The linguists of the Moscow Phonological School represent the morphological approach to the problem of establishing the phonemic status of a sound in neutral position.
According to this approach, to establish the status of a sound in a phonologically neutral position, one should find an allomorph of the same morpheme in which the phoneme under question occurs in the strong position (i.e. in which it retains all its DFs).
The Moscow linguists are of the opinion that interchange of sounds shows close connection between Phonetics (the science of the sound system) and Morphology (which studies grammatical meanings).
Alternations take place in one and the same morpheme and reveal its phonemic structure. The phonemic content of the morpheme is constant according to the Moscow Phonological School.
The definition of the phoneme proposed by the Moscow Phonological School: "a functional phonetic unit represented by a row of positionally changing sounds".
According to the authors of "English Phonetics. A Theoretical Course" (M.A. Sokolova et al) the advantage of the morphological conception is in that "the alternations of the phoneme are not analysed apart from the morpheme, as form and content make dialectical unity. The phonetic system is not isolated from the grammatical and lexical structure of the language" [Sokolova et al 1996: 98].
The relations between different sounds representing one and the same phoneme are called interallophonicby the linguists of the Moscow School.
The same relations are defined as interphonemic by the representatives of the Leningrad Phonological School. The linguists of this trend support the autonomous approachto the phoneme: the autonomy of the phoneme and its independence from the morpheme (different allomorphs of a morpheme may differ from each other not only in their allophonic, but also in their phonemic composition).
The archiphoneme theory(elaborated by N.S. Trubetzkoy):
In the position of neutralization one can speak of a unit higher than a segmental phoneme - the archiphoneme is a combination of distinctive features common to two phonemes; or in other words, the archiphoneme consists of the shared (common) DFs of two or more phonemes but it excludes the feature which distinguishes them.
Many linguists share the approach to the phoneme status suggested by acad. L.V. Shcherba(1880 -1944)who defines the phoneme in the following way: "ů in actual speech we utter a much greater variety of sounds than we are aware of; in every language these sounds are united in a comparatively small number of sound types which are capable of distinguishing the meaning and the form of words; that is, they serve the purpose of social intercourse. It is these sound types that we have in mind when discussing speech sounds. Such sound types will be called phonemes. The various sounds that we actually utter and which are the individual representing of the universal (the phoneme), will be called phonemic variants" [┘ňßÓ 1963: 19].
V.A. Vassilyev develops Shcherba's conception. In "English phonetics: a theoretical course" one can find the definition: "The segmental phoneme is the smallest (i.e. further indivisible into smaller consecutive segments) language unit (sound type) that exists in the speech of all the members of a given language community as such speech sounds which are capable of distinguishing one word from another word of the same language or one grammatical form of a word from another grammatical form of the same word" [Vassilyev 1970: 136].