Words in the structure of sentence expresses conceptions, which are correlated with existed reality, are formed with the concrete affixes of different grammar categories, which characterize their relations and connections at the defined syntactical structure. Therefore, they have semantic, grammatical and functional meaning.
In modern linguistic science there are different theories concerning what is the member of sentence and what status it has inside the communicative and predicative syntactical unit. While the definition of essence of sentence´s member close to all their disagreements the majority of researchers consider that the functional part is principle - one word at the structure of sentence can be subject, predicate etc, it depends on what syntactical function it has in these concrete case. While the definition of status of sentence´s member (main and secondary) there are a lot of disagreements between the researchers.
A number of researchers consider that conceptions "The main member of sentence", "the secondary member of sentence" still have no rather clear definition in the grammatical system of language. For example, A. A. Holodovich wrote that "such hierarchy (main, secondary) originaly existed, apparently, as the result of compromise between purely logical and perely linguistic view to the essence of sentence: sentence represents judjement (in that appearance, in which it were understood by the logic), and all that represents judgement is the principle in the sentence; all that is singled out in the sentence that not based on the logic foundations is secondary..." [3; 293]. On the other hand famous syntaxist V. A. Beloshpakova affirmed that " differential sign, at the base of which the members of sentence are traditionally divided into main and secondary, is entry or nonentry to the predicative base of sentence, participation or nonparticipation to its creation" [4; 84].
To summarize existed basic syntactical propositions about qualification of sentence´s members one can single out three conceptions: a) conception of unimodality of sentence, b) conception of multimodality of sentence.
In traditional grammar the conception of multimodality of sentence (presence of two main members - subject and predicate) affirmed long time ago . This conception is considered to be a base not only for European (particularly Slavonic) languages, at the material of which was developed the theory about main and secondary members of sentence, but for Iberian-Caucasian, particularly Abkhazian-Adyghe, normative grammar of which was developed at the base of theory of multimodality of simple sentence [6,7].
There are other conceptions in syntactical theory, particularly when the main member is only subject (or only predicate), and, on the contrary, when to the main members of sentence refers direct (and sometimes indirect) object.
The conception of unimodality of sentence has two varieties. First affirms that "subject is always primary word in the sentence" [8; 70] and stands absolute or independent definiendum and doesn´t act like a definition to any other word" [9; 27]. F. F. Fortunatov defined subject as independent by meaning part of word combination, and predicate - as dependent "part of finished word combination" [10; 183]. Opposite opinion have A. A. Holodovich, S. D. Kacnelson and others. S. D. Kacnelson wrote that "dominance" of predicate is provable in contrast to subject and that "in substantial plan verb predicate is more than lexical meaning. Expressing defined meaning, it at the same time contains a model of future sentence" [11; 88]. In Abkhazian-Adyghe linguistics the conception of unimodality of sentence (in the variant: only predicate is the main member of sentence) is found in the works of U. S. Zekoh .
The contrast of the conception of unimodality of sentence is the syntactical theory, which makes the status of main member of sentence not only to subject and predicate, but to the object too (basically to direct object, but sometimes to indirect one too). This theory in some modification is represented in the works of famous linguists N. F. Yakovlev and D. A. Ashhmaf , Z.I.Kerasheva [14; 9-52], B. H. Balkarov [15; 22-28], R. N. Klychev [16; 127-160], H.K.Aristav  and others.
The complexity of qualification of some members of sentence as main and as secondary in Abkhazian-Adyghe language is connected with the peculiarities of ergative construction, and, therefore, with the essence and structure of transition verb in these languages. If we don´t strive for the deep analysis of peculiarities of different classifications of sentence´s members, the subject will be found as one of the principle elements of semantic and structurally grammatical organization of sentence in any of afore-cited conceptions. In the thirties of XX century professor A.N.Genko wrote, that "its (sentence´s) composition includes as a minimum two members: that one, which expresses itself the view of object or person and is named as subject of sentence, and another one that expresses itself the view of sign (or the sum of signs), which is connected to the subject, is named as predicate..." [6; 190].
The subject in syntactical theory often is defined semantically. Generally it can be formulated as: the subject is the member of sentence, which expresses subject [18; 478]. But "interpretation of subject through the conception of subject is the explanation one unknown through another, because the conception of subject provided to be fuzzy and indirect. We can find not less variety of subject than types of subject: there are distinguished subjects of motion, condition, sensory perception, and also grammatical, logical, psychological" [19; 178]. The majority of existent definitions are combined to the following: subject is the compulsory member of sentence (word, word combination or other syntactical construction), which has grammatical semantics of subject that is defined in sentence with the help of sign - predicate.
By its meaning, occupied position in the sentence and ways (facilities) of expression the subject in Abazin language has different descriptions.
Clearly that in modern Abazin language names are not declined, there is no grammatical category of case, and that is why grammatical relations between subject (as object) and predicate are formed with the help of class-personal affixes. Between the verb-predicate, on the one hand, and subject (direct and indirect objects), on the other hand, "exists steady double-sided connection:
а) person, class and number of verbal indicators of grammatical subject and object depend on person, class and number of direct and indirect objects that attend in the sentence;
b) the possibility of attendance direct and indirect objects in the sentence, in turn, depends on structure of verb-predicate: if there exist signs of direct and indirect object, they will be able to exist in the sentence as its individual members; if in the verb-predicate there are no signs of direct and indirect objects, they will not be able to exist in the sentence" [16; 135].In other words, subject, direct and indirect objects and their proper signs (of subject, direct and indirect object) agree with in the person, number and class in the absolute majority of cases. Subject (and also objects), on one hand, directs grammatical form of predicate (predicate agree with subject), on other hand the essence of verb-predicate defines the possibility of appearance in the structure of simple sentence of direct and indirect objects. This "steady double-sided connection" between the subject, objects and predicate academician A. S. Chikobava at the beginning of XX century offered to name "coordination" [20; 243], later this term was used by other linguists (Shvanskii, Raspolov, Tihonov and others). There exist other names of this type of connection : "coupling" (Zolotova G.A.), "predicative connection" (Muhin A. M., Aristava H. K).
Structure and grammatical analysis of simple sentence of Abazin language gives us grounds to say, that objects (both direct and indirect) by their grammatical characteristics in the structure of sentence are almost not differ from the predicate: they also govern the form of predicate with the help of class-person formant, they also occupy the same places that subject occupies, they are also expressed by the same parts of speech and as the subject does they are also have no special grammatical form etc. Thereby famous linguists recognized the conception of multimodality of sentence to be more corresponded peculiarities of sentence in Abkhazian-Adyghe languages.
But, while all aforesaid peculiarities of sentence in Abazin language, we can´t but mention the main thing - in contrast to object the possibility of appearance in the sentence apart expressed (by word or syntactical construction) subject doesn´t depend on essence of verb-predicate - it (subject) occupies its syntactical position both while transitive and intransitive verbs-predicates. Subject, as predicate is, is the independent member of sentence that is not dependent (about presence and absence) on any other structural component of communicative and predicative syntactical unit. Hence main members of sentence in Abazin languages should be recognized only subject and predicate. They should be recognized as structural base of simple sentence in Abazin language, though forming components are undoubtedly both direct and indirect objects.
Subject in the simple sentence of Abazin language can be placed at the beginning, in the middle and at the end of predicative-communicative unit, its syntactical position was not fixed, but it more draws towards the beginning of sentence.
While the transitive verb-predicate the usual order of words in the sentence is like this: subject - indirect object - direct object - predicate, what represents mirror reflection of succession of their class and person signs (formants) in the structure of transitive predicate. ГIвыджь наскIьан атшы агъвра ахъарцIатI «Two came up and put on the horse the bridle». In these case subject гIвыджь «two» occupies absolute beginning of sentence, and its class and person formant -р- (3-е л. мн. ч.) stands between two parts of complicated base of predicate й-а-хъа-р-цIатI «put on it », after the signs both of direct (й-), and indirect (-а-) objects.
While the intransitive verb-predicate the order of words in the sentence and their formants in the structure of verb concur: the subject draws towards the beginning of sentence, and its formant stands in absolute beginning of corresponded predicate, indirect object (or indirect objects) follows after it and occupies position between subject and predicate, its formant stands after the sign of subject before the base of verb. Асаби ачIва дацхIатI «Child nibbled at apple ». Subject асаби «Child» occupies syntactical position of beginning of sentence, and its sign д- (3rd person, singular) also stands in absolute beginning of predicate д-а-цхIатI «nibbled at». Indirect object ачIва «apple» stands after the subject, its formant -а- (3rd person, singular, class thing) stands after the sign of subject.
The subject can carry different types of definition, absolute majority of which are prepositive. Therefore in these cases formally the subject doesn´t stand at the absolute beginning of sentence - it follows before the attribute (single or whole combination, and sometimes expressed with infinit construction). But in these situation between the base members of sentence (subject, direct and indirect object, predicate) it (subject) provided to be the nearest to the absolute beginning of sentence. Йдучвам апещ угIала йырчвын «Small room was full of people». The position before subject or absolute beginning of sentence is often occupied by adverbial modifier. Ауат зымгIва хIанрылга ачвква ацIахIхIвахын хIгIаджвыквылхтI «When everyone had finished it, we harness the bullocks and left home».
Thereby, both while transitive and intransitive verb-predicate the most usual place of disposition of subject in Abazin language is the position of beginning of sentence. The rest of positions (middle and end of sentence) are occupied rarely by the subject of Abazin language, but these positions are not impossible or breach of offer of words in the sentence.
In modern Abazin language the subject is more often expressed by the noun, substantivized adjective or participle and also pronoun. Other parts of speech can be also realized in the syntactical position of subject, but occur very seldom.
The syntactical position of subject can be occupied by word combinations, infinit constructions, phraseological units, and also the whole sentence, which is singles out as a whole syntactical construction in the composition of simple sentence. All of them have their own peculiarities while the realization of facility of subject, but occur much more seldom than afore-cited.
The subject in the modern linguistic literature that is devoted to the problems of syntax is often defined differently. «Firstly, discrepancy and insufficient clarity of theory of predicate are conditioned by that in linguistic tradition as in Russian one and in foreign there are exist two approaches to the understanding of essence of predicate. According to one of them as the predicate can single out only finite verb, and connected with it infinitive can correspond only supplementary verb member (Shahmatov). In compliance with other approach the subject includes not only finite verb but also dependent on it infinitive (Ovsyanico-Kylikovskii)... Besides, there is no united approach to the formal varieties of subject, to the classification of verb constructions. So to single out the types of English predicate we should choose one of the following sign: the structure of predicate (Vynikurova; Ganshina and Vasylevskaya; Gygadlo and others; Haimovich and Rogovskaya), morphological belonging of its principle part (Ivanova and others; Irtenyeva), or both signs at the same time (Ilyish), or structure and semantic (Barhudarov and Shteling; Smirnickii, 1957)» [19; 183-184]. Terminological confusion occurs often - there are found cases, when the same phenomenon has different terms and on the contrary different linguistic phenomenons are expressed in one term by different authors. All these complicate the definition of essence of the predicate and its semantic and structure and grammatical peculiarities in different languages.
In these work we act on the premise that in "the realty there are double-essence phenomenons: on the one hand there exist objects, things, but on the other hand there exist actions of these objects and things... Use in role of predicate the nouns that mean the ideas of things and the verbs that mean actions gives us an opportunity to characterize the object (subject of sentence) from two different sides, from the side of its behavior or signs, the bearer of which is the object, and from the side of action, which are accomplish by it" [21; 3]. Hence it is reasonable to subdivide predicates into two basic types - verbal and nominal. Such classification accents our attention not only on semantic side of word (or words), which plays syntactical function of predicate, but also takes into consideration grammatical peculiarities and possibilities of this word. For example, in Abazin language the function of predicate can be done not only by auxiliary finite verb, but also by denominative one, which, as the derivative from the nominal part of speech, by its structural and grammatical characteristics are not differ from static verb, due to its own klass and person prefixa and so-called suffix of predicativity. This suffix is the formant of time category, finiteness and static nature at the same time.
Predicate in Abazin language, while expressing modal-time an subject-object relations, is organizing center of sentence. In it, as it was noticed by the researcher of Abkhazian language H.K.Aristava, "grammatically concentrated syntactical functions both nominal and erbal components of sentence of another languages (for example, Russian)" [17; 122].
The main syntactical position of predicate in Abazin language is the end of sentence. But it doesn´t mean that predicate can´t occupy other syntactical position. Depending on its semantic meaning, urgent segmentation, peculiarities of speech´s organization (rhymes in poetic works) predicate can be situated both at the beginning and in the middle of sentence. Last in the absolute majority of cases is conditioned.
The main form of expression of predicate is the verb that due to its polysynthetic essence has big syntactical opportunities. But not any verb (not all existing in modern Abazin language grammatical forms of verb) can play the role of predicate. The main verbal form, which occupies syntactical position of predicate, is finite verb. It can be dynamic or static, transitive or intransitive, auxiliary or denominative. The function of predicate can be made by infinite-interrogative forms of verb. The rest of verbal formations (infinite verbs and infinite constructions) can´t express time independently, are not used used in syntactical position of predicate in Abazin language (except cases, which are conditioned by context, situation) because that they don´t have defined semantic and completed meaning.
By its structure and component composition predicate in Abzin language can be simple or composite. Predicate is simple when grammatical and substantial meaning that are some of its basic characteristics as the member of sentence are expressed by one word. Such in Abazin languages are finite and infinite-verbal verbs. Адгьыл зырхарджьуа йчIвыпI «Acres belong to that who work it». Ахча зщарду агъыч дичвшвитI «Who have a lot of money is afraid of thieves ». Уысасчваква анбацах, Абдулкьарим? «When your guests left, Abdulkerim?». «Швыпхын атшпсщара мшква шпажвга?» - лхIван арыпхьагIв асабиква дырцIгIатI «How did you pass your holidays?» - teacher asked her pupils».
In the cases when substantial meaning is expressed with one word (or with form of word), and grammatical meaning with other word (as usual by auxiliary component) predicate is called composite. In modern Abazin language composite predicates can be verbal and nominal.
The ideal form of expression of simple predicate is finite verb. While this, dynamical verbs (both ordinary and relative) make their syntactical function in seven verbal-tenses forms of indicative mood, syntactical ones - in two forms.
Simple verbal predicate in Abazin language can be also expressed by other finite forms of verb - admitable, imperative, optative, subjunctive, hypothetical moods and by different interrogative forms.
In the syntactical position of simple verbal predicate are also natural interrogative forms of verb, and it can be not only interrogative forms of finite verb with the indicative semantic, but also verbs of infinite-interrogative formation (adverbial-verbal and relative-interrogative), which is not natural for affirmative not interrogative verbal forms. Proper formations have their own grammatical and function peculiarities, what can be object of other research like composite (nominal and verbal) predicate.
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 In the special literature there exist other classifications and also occur other terms. For example, P. A. Lekant prefers terms "simple predicate" and "difficult predicate", what is really justified, if we take into consideration the great number of forms and structure types, which belong to composite predicates. The researchers of Adyghe languages H. E Djasegev, B. M. Kardanov, H. H. Urusov, A. M. Kambachokov at the material of Kabardinian language single out three types of predicate: simple, composite, compound [7; 180] etc.
 Analogous forms at the material of closely related Abkhazian language are detailed described by H. K. Aristava [17; 122-133].