Grammatical Approaches to Prepositions , Adverbs , Conjunctions , and Particles in Late Modern English

Current shift of linguistic paradigms and loss of interest in previously mainstream ‘parts of speech theory’ do not imply that all ambiguity and outstanding issues have been challenged and successfully solved. On the contrary, these issues have been put on pause, as linguists, coming to naught and being unable to set forward a univocal, straightforward solution, started refocusing their scientific pursuits. Nevertheless, the problem of parts of speech overlapping has remained of vital importance, even if it is in the background of linguistic research. This issue must be addressed from the theoretical and practical perspectives. The present study attempts to give a theoretical overview of grammatical approaches to prepositions, adverbs, conjunctions, and particles which were prevailing in the Late Modern English grammar. The analysis is based on 400 English grammar books, published over the period of Late Modern English, and is divided into three sections in conformity with certain historical periods, viz. 1700–1799, 1800–1849, 1850–1899, respectively. The research presents the major tendencies towards identification of the aforementioned categories, which characterize each historical period in English grammar and explain the current state of affairs in the parts of speech theory, providing theoretical background for further practical research on the parts of speech overlapping.

The Late Modern English period has been chosen because it is not only the "age of prose" (Gordon, 1966, p. 133) and the "golden age of letter writing" (Arnaud, 1998, p. 125), but "a great age for dictionaries and grammar books in England" (Romaine, 2007, p. 8). Ostade (2009) asserts that "from the 1750s onwards, all kinds of manuals appeared for people with social aspirations, especially grammars and pronouncing dictionaries. Around this time, we see the beginnings of what today is called the age of prescriptivism, the final stage in the standardisation process of the English language, which started in the fourteenth century" (p. 3). Robins (2013) emphasizes that "the eighteenth century in Europe saw some very significant developments in linguistics" (p. 152). The grammar books published in 1700-1900 form a unique linguistic layer, which, as Davies and Lepschy (1998) formulate, "abandons earlier theoretical discussions in favour of a more empirical and historical approach using new methods to compare languages and to investigate their history" (p. 1). So, this period attests the final stage in earlier linguistic studies and, at the same time, is the inception of all modern theories and approaches in linguistics.
The research is based on the analysis of 400 English grammar books, published during the so-called "age of standardization or prescription stage" (Hogg & Denison, 2006, p. 284), among which the readers may find the works by Walker Sweet (1892), and Nesfield (1898), to name but a few. The choice of this historical stage is also substantiated by the heterogeneous nature of the Late Modern English grammar in which there are "more than 30 different modifications of the PoS system" (Kovbasko, 2020, p. 41).
All the sources have undergone thorough manual analysis aimed at distinguishing each part of speech individually, their characteristic features, peculiarities, etc. The predominant approaches have been synthesized and organized diachronically to make a linear flow. The paper is divided into 3 sections, which describe certain historical periods: the 18 th century, the first and the second half of the 19 th century. The analysis of the 19 th century is halved into 1800-1849 and 1850-1899, respectively, due to an upsurge observed in linguistic studies and an abundance of grammar books printed during this period.
The novelty of the paper is explained by the in-depth study of the approaches to prepositions, adverbs, conjunctions, and particles in Late Modern English, which forms a unique compendium of the ideas that predominated in the 18 th and 19 th century grammars. As a result, the research lays feasible and relevant foundations for the development of modern areas in linguistics, for example, universal grammar "the basic philosophical attitude of which persists in British thinking about language to the end of the eighteenth century, and no doubt beyond" (Jones, 2015, p. 4).
The research is carried out in the frames of descriptive analysis, according to which, all major theories, ap-Methodology proaches, views on prepositions, adverbs, conjunctions, and particles in all the grammar books under study are extracted, analysed, described, and structured. The study enters the sphere of bibliographical analysis and literature review (see Esquirol-Caussa et al., 2017), as it takes into account the scientific knowledge and relevant bibliographic sources of a given topic.
Throughout the development of linguistic ideas in the English language, its grammatical system has been influenced by various external factors, in particular dominance of Latin and French. Nevertheless, the biggest concern is not the influence of these languages, because English has managed to retain its own peculiarities and features, but the way grammarians and theoreticians have tried to impose those extra-linguistic factors on English. It can especially be observed within the closed class of words filled with functional units, which lie at the origin of the English language and could hardly be substituted or changed throughout the course of the language evolution. To my mind, this situation has led to ambiguity, inconsistency, and confusion that is currently perceived within the closed word classes and, what is more, between the units of the closed and open word classes. On the one hand, the problem is concealed in the adverb paradigm as a representative of the notional parts of speech. Some grammarians observe a dramatically heterogeneous nature of the adverb category that "can only be considered as a receptacle for all straggling, non-descript and unclaimed words, but which are of too multifarious a character to admit of either rule of definition" (Lyon, 1832, p. 218) or is "the common sink and repository of all heterogeneous and unknown corruptions" (Leonard, 1907, p. 213). The nature of the category, where one lexical unit due to its various characteristics may belong to any other word class, leads to further functional transposition. On the other hand, the connective nature of prepositions and conjunctions has always confused grammarians. Thus, it is necessary to gain insight into the classes of adverbs, prepositions, conjunctions, as well as particles, which is often interpreted as the category embracing items that belong to the aforementioned parts of speech.

Historical Overview of the 18 th Century
In general, "it was rare for Latin to be rejected as a model" (Allan, 2009, p. 145), so English grammar books in the 18 th century are characterized by a tendency to provide strict definitions of adverbs, prepositions, and conjunctions, mainly focusing on their denomination and connection with other words, as it was observed in Latin grammar. An adverb is commonly defined as "a word that is joined to a verb, or an adjective, to participle or another adverb to denote some circumstance, some quality or manner signified in them" (Greenwood, 1737, p. 96). This definition is supported by the majority of linguists (see Coar, 1796;Mackintosh, 1797;Lowth, 1799). The ability of adverbs to be joined to nouns causes disputes, because some grammarians (see Turner, 1710;Rudiman, 1755), following the Latin tradition, insist on it, whereas others mention that adverbs "denote circumstances which coalesce with what is partly expressed by a verb or adjective, but not with what is partly expressed by a substantive" (Ward, 1767, p. 72). In the course of time, the former point of view has decayed, as the connection with substantives becomes a conventional and exclusive prerogative and a leading characteristic of prepositions. What is common for almost all definitions is the chief signification of adverbs: time, place, number, quantity, affirming/consent, denying, doubting, certainty/confidence, comparison (see Greenwood, 1737), or modification/ circumstance of an action, manner, order, time, place, distance, relation, quality, quantity, comparison, doubt, affirmation, negation, demonstration, interrogation (see Lowth, 1799). These observations show how diverse the adverb category is and why it is so difficult to produce a unified approach.
Within this period, prepositions are generally defined as words that "serve to connect other words with one another and show relation between them" (Lowth, 1799, p. 94). Keeping in line with the Latin grammatical tradition, Turner (1710) insists on the obligatory presence of cases of words governed by prepositions, while Rudiman (1755) and Perry (1795) identify these words as nouns and pronouns. Much attention is devoted to the connective force of prepositions, which, according to Harris (1751), unites the words that refute to unite themselves. In this regard, Ward (1767) speculates that the use of prepositions is the reflection of certain connective operations of the mind to the conceptions denoted by substantives and Greenwood (1737) even calls them "the nerves and

Results and Discussion
ligaments of all discourse, […], which show respect or relation one thing has to another" (p. 104). These remarks play an important role in distinguishing prepositions and adverbs, but make their interpretation closer to conjunctions. Such combination of two grammatical restrictions, viz. grammatical power to combine lexical items and the presence of a substantive to the right of prepositions, is aimed at preventing transposition between the classes. For example, prepositions are easily converted into adverbs when they totally lose their connective nature or are put without a case after them (see Turner, 1710;Harris, 1751). According to the linguists, to remain a preposition, any lexical unit must connect two items, one of which is a noun/pronoun/noun phrase. However, the idea of an obligatory 'physical' presence of a noun complement is questioned by Coar (1796), who states that "preposition is a word put before another to which it is applied in order to show the relation of such word to some other word either expressed in the sentence or understood" (p. 129). To my mind, such an approach is of great significance, because instead of a noun complement different alternative complements or even no complements can be used, cf., Huddleston and Pullum (2012), Kovbasko (2016).
The major characteristic of prepositions and adverbs, which gives them a common ground with conjunctions, is the ability to connect other elements. Overlapping between the categories is mentioned by Turner (1710), who notes, that "several of these here reckon'd among the conjunctions may also be called adverbs" (p. 34). The idea is also discussed by Harris (1751) and Rudiman (1755), who note that the same words can be found among the categories of adverbs, prepositions, and conjunctions. Moreover, Harris (1751) elaborates the term 'adverbial conjunctions' and combines conjunctions and prepositions into the class of connectives what, in fact, intensifies the ambiguity between these categories.
Trying to distinguish between prepositions and conjunctions, the grammarians in the 18 th century define the latter either as 'parts of speech' (see Lily, 1709; Greenwood, 1737), 'words' (see Turner, 1710; Priestley, 1772), or 'particles' (see Philipps, 1731), whose first service is to join words in sentences, parts of sentences or sentences together (see Ward, 1767; Webster, 1790; Perry, 1795; Coar, 1796). Another approach is elaborated by Harris (1751), who presumes that conjunctions do not connect words, but sentences and meanings, showing the manner of their dependence upon one another (see Greenwood, 1737; Priestley, 1772; Mackintosh, 1797).
Another way of analysing adverbs, prepositions, and conjunctions lies within the category of particles. It is necessary to admit that the notion of particles is not clearly defined either in the 18 th century or nowadays. Thus, Philipps (1731) defines particles as "words that signify some manner, circumstance or connexion of words and sentences and can neither be declined nor conjugated in good sense. Here belong adverbs, prepositions and conjunctions" (p. 17). Greenwood (1737) treats particles as little parts of speech and Walker and Tooke (1720) unify all short words (articles, prepositions, numerals, etc.) under the name of particles. Webster (1790) proposes to single out particles or abbreviations as "a separate part of speech, including adverbs, conjunctions and prepositions, which are used to connect nouns, verbs and sentences, adding that they were formed last in the progress of language" (p. 8). Such a definition slightly resembles that of Philipps' (1731) as it combines everything functioning under the names prepositions, conjunctions, and adverbs into one category. Lowth (1799), on the contrary, rejects these ideas, describing particles as words which cannot stand by themselves in constructions, e.g. 'a', 'be', 'con', 'mis', etc. To my mind, this definition corresponds with inseparable prepositions, as 'a' and 'be' are, in fact, Old English prepositions that have undergone grammaticalization.

Historical Overview of the 19 th Century: First Half
Grammatical approaches to adverbs in the first half of the 19 th century predominantly follow the same line as in the 18 th century, defining adverbs as "parts of speech joined to a verb, an adjective and sometimes to another adverb to express some quality or circumstance respecting it" (Murrey, 1805, p. 119). Linguistic research on PoS, however, stimulates elaboration of definition and general understanding of the category. For example, Ash (1810), Greenleaf (1823), Smith (1834), and Turner (1840) state that adverbs can modify participles. The ideas concerning possible modifications of nouns by adverbs, proposed by Pommeraye (1822) and Alexander (1835), stand apart and seem to be just a linguistic calque from Latin, cf., Grant (1808) and Edwards (1830). The specification that adverbs can qualify verbs, adjectives, adverbs as well as prepositions and articles, which is provided by Putnam (1828), sounds like an attempt to combine every possible signification in one definition and is a simple demonstration that the category of adverbs is unreasonably outsized.
Classes of adverbs, to a greater or lesser extent, remain the same, e.g., number, order, place, time, quantity, manner/quality, doubt, affirmation, negation, interrogation, comparison, etc. Despite all similarities in defining adverbs some new grammatical approaches are established in the first half of the 19 th century. First of all, adverbs are defined as "contractions of sentences or parts of sentences, generally serving to denote some circumstances or manner of an action added to verbs, adjectives or other adverbs" (Harrison, 1812, p. 35). The idea is supported by Morgan (1814), Pommeraye (1822), Cardell (1827), Crombie (1830), who interpret adverbs as abbreviated expressions, phrases or sentences, corruptions of other words, compound or contracted words, used to express compendiously in one word what must otherwise have required two or more words. Bosworth (1826) draws attention to formation of adverbs, stating their substantival or adjectival nature in certain cases. To my mind, such specifications help to distinguish between prepositions and adverbs, and the key issue of such abridgements lies in speakers' cognitive processes and striving for language economy of efforts. By means of adverbs (those in use or newly-coined), speakers try to reduce efforts expended in the course of communication, efforts needed to compose, reproduce, and comprehend a phrase. This leads to a notion of the so-called separable adverbs, which are the examples of language economy, e.g., in vain -in vain 'manner', by far -by far 'extent', in quiet -in quiet 'tone', etc., when adverbs become signs of more complex ideas resolved into more simple terms (see Cramp, 1838; Hunter, 1848). Another significant conclusion, made by the linguists in the first half of the 19 th century, is determination of an adverb as a secondary and optional part of speech, which forms "by no means the least important of the nine distinct parts of speech" (Cardell, 1827, p. 144). I suppose that, being a secondary part of speech, adverbs did not appear in the language at the very beginning, so their nature is purely cognitive and they come in use or are coined only when the necessity arises (this does not refer to primary adverbs of time and space). Moreover, forming a large class of coreless words, being used with verbs, adjectives, and participles, adverbs can be easily omitted without any damage to the deep structure of sentences.
The general definition of prepositions remains unchangeable, but the number of specifications is introduced. Firstly, the emphasis is put on the name of the category, which is "called so from two Latin words meaning before and place and this name is given them because they are in most cases placed before nouns and pronouns" (Cobbett, 1835, p. 32). Secondly, linguists focus on words prepositions govern, are joined to or stand before, mentioning the presence of cases (see Ash, 1810; Jamieson, 1826; Rask, 1830; Del Mar, 1842). With increasing frequency grammarians start describing the conjunctive nature of prepositions, emphasizing that they connect ideas, objects, and/or notions (see Fearn, 1824; Cardell, 1827; Turner, 1840; Hunter, 1848), i.e., a shift from the lexical to the semantic level is observed.
Another widespread tendency is to provide full lists of prepositions (see Murphy, 1800; Morgan, 1814; Jamieson, 1826), to simplify interpretations of the category. Under the influence of the Latin grammar such classifications are based on the phenomenon of cases. The linguists explain that one of the great uses of prepositions in English is to express those relations which are chiefly marked by cases or different endings of nouns, i.e., to supply the need in cases and deficiency of the inflections commonly called cases (see Murrey, 1805;Morgan, 1814;Jamieson, 1826). In order to prove the theory, many grammarians specify the cases, e.g., 'objective case' (see Ussher, 1803; Lyon, 1832; Smith, 1848), 'accusative or objective' (see Adam, 1820), 'accusative or dative' (see Bosworth, 1826) 'all types of cases' (see Grant, 1808; Rask, 1830; Del Mar, 1842). Taking into account the lack of cases in Middle and Modern English, it is worth noting that grammarians imply the use of prepositions in Old English.
In the early 19 th century, the notion of stranded prepositions, i.e., a non-canonical word order, in which a prep-osition and its object, e.g., noun phrase, are not adjacent (Ursini, 2015), becomes more or less formed. At that time, grammarians express much prejudice against such constructions, interpreting them as the instances of vulgar and incorrect language; for example, Ussher (1803) denotes that "the mode of ending the sentence with a preposition is an idiom to which our language is wrongly inclined; yet it seems to be studiously avoided of late by many respectable authors; and indeed it is censured by some of our best grammarians" (p. 51). Nevertheless, the non-canonical position of prepositions in sentences is being researched, especially in Old English grammar, where the examples of prepositions separated from the words they govern and emphatically placed before the verb in a sentence are numerous (see Bosworth, 1826). This is not a direct example of stranding, but it exemplifies the idea of using prepositions not before the words they govern, which is profusely implemented in Old English.
In the first half of the 19 th century, conjunctions are defined either as 'parts of speech' (see Murrey, 1805 Pommeraye, 1822), 'words and propositions' (see Andrews and Stoddard, 1840), and even 'notions or thoughts' (see Hunter, 1848). These approaches testify deviation from a clear syntactic designation of conjunctions to the analysis of conjunctions at the discourse level and their power to connect mental units. Another factor that adds to ambiguity is the idea that "a conjunction requires a whole sentence, either expressed or understood, to complete its function of connexion" (Doherty, 1841, p. 74), as it represents the ability of conjunctions to join sentences, one of which is not represented 'physically', but implied. To some extent, it resembles the approach to prepositions, which can be used without 'physical' complements.
Therefore, the syntactic factor prevails in distinguishing conjunctions in the 19 th century. At the same time, the semantic approach allows to single out a variety of subcategories, cf. Adam (1820) -14; Crombie (1830), Andrews and Stoddard (1840) -9; Alexander (1835) -6; Doherty (1841) -4; Murrey (1805), Harrison (1812), and others -2 subcategories. The identical division is observed in the 18 th century, but now it becomes predominant. Nevertheless, in the early 19 th century, a new approach, based on the syntactic division of the category, appears. Murphy (1800) suggests distinguishing conjunctions in accordance with the syntactic approach, naming coordinate and subordinate conjunctions, which, in their turn, are divided into subtypes on the basis of the semantic factor. To 'coordinate' conjunctions belong copulative, adversative, alternative, illative, and among 'subordinate' one can find conjunctions of cause, conjunctions of time, conjunctions of place, conjunctions of comparison, conjunctions of purpose, and conjunctions of manner. In the first half of the 19 th century, this approach does not become widespread, due to various semantic classifications, which have already rooted and become traditional. Another factor is an extensive use of the two-element classification -'copulatives/continuatives' and 'disjunctives'. It is worth mentioning that along with the syntactic and semantic classifications there is a morphological division, i.e. according to the form, under which correlative conjunctions are singled out. In this case, it is also possible to speak of morpho-semantic division, as the main characteristic of the subcategory is the paired form (two conjunctions are used in pair and in semantic correlation with each other). Another example is the division of conjunctions into simple and compound (see Grant, 1808; Rask, 1830).
Hence, the category of conjunctions is described on the basis of three key factors -form, meaning, and function, which are not applied simultaneously to understand the whole concept of the category, but rather at different stages. The general definition of this category is grounded on the syntactic approach, subdivision into subcategories is based on the semantic and partially morphological factors, and functions are presupposed by semantic and syntactic features. This contributes to ambiguity in defining parts of speech. In particular, it is mentioned that many words belonging to other parts of speech are used as conjunctions, viz. verbs, adjectives, adverbs, prepositions, and pronouns (see Ussher, 1803;Putnam, 1828;Lyon, 1832). It gives a possibility to discuss two approaches: firstly, featuring the same lexical units as representatives of different parts of speech; secondly, the ability of lexical units to function as representatives of different parts of speech. In any case, it raises the issue of the etymology of these lexical units, necessity to identify their primary forms, functions, and meanings. From the theoretical perspective, it contributes to the development of a 'benchmark' or primary classification of parts of speech. From the practical perspective, it showcases shifts within the PoS system and represents the vector of further development of the English language. Thus, it is substantiated to apply the etymological approach to the analysis of transposition between the categories of adverbs, prepositions, and conjunctions.
The notion of particles is not unified at this period; for example, Gilchrist (1816) remarks that the category of particles comprehends articles, pronouns, prepositions, and conjunctions, Rask (1830), Andrews and Stoddard (1840) designate adverbs, prepositions, conjunctions, and interjections among particles, Cramp (1838) names only prepositions and conjunctions, whereas Hildreth (1842), on the contrary, excludes prepositions from particles, and refers only adverbs and conjunctions to this category. Less standard approaches identify coalescence of particles and prepositions (see Doherty, 1841), particles and inseparable prepositions (see Crombie, 1830; Greene, 1830; Webster, 1843), or particles and adverbs, broken words, contractions (see Cardell, 1827). These numerous studies show that in the first half of the 19 th century there is no strict interpretation of the category of particles and units which belong to it.

Historical Overview of the 19 th Century: Second Half
In the second half of the 19 th century, the approach that "under the head of adverbs can be included every word that does not clearly belong to some one or other of the parts of speech" (Lyon, 1832, p. 122) or that "the class of adverbs is the final resting-place of waifs and strays -the depositary of odds and ends of language" (Ramsey, 1892, p. 477) becomes firmly established. The most popular and general definition of the category, however, remains unchanged, representing the ability of adverbs to modify the meaning of a verb, an adjective, or another adverb. The developments in the PoS theory, which take place in this period, provide new perspectives on the classes which may be modified by adverbs, adding to them 'participles' (see Bullen, 1870), 'infinitives and prepositions' (see Welsh, 1889), and 'verbals' (see Lyte, 1899). Moreover, grammarians start testifying new functions of adverbs, stating that they are used to modify 'a phrase or an entire proposition' (see Kerl, 1867), 'adjunct or the whole idea' (Quackenbos, 1873), or 'the sense of a complete clause or a sentence' (see Bartlett, 1899). To my mind, these refinements provide evidence, which helps to distinguish between adverbs and prepositions, especially when two prepositions are used together. In such cases, grammarians often refer to the first lexical item as an adverb, because one preposition cannot follow another.
Concerning previous observations, more and more grammarians continue interpreting adverbs as contracted, elliptical, or abbreviated substitutions for phrases, clauses, and sentences, which may in one word express what otherwise would require several words (see Kenny, 1858;Clark, 1862;Lewis, 1872). This approach shows that adverbs are commonly compounded of some other words, and form a secondary, additional part of speech, which appeared in the language after the fundamental classes, in particular, nouns, verbs, and prepositions. In fact, in the grammar books of this period, many lines are devoted to the etymology of adverbs and ways of their formation. According to the research, the category of adverbs is formed on the basis of various combinations of demonstrative pronouns, nouns, verbs, prepositions, adjectives, and individual letters (see Kirkham, 1855; Barrett, 1861; Smith, 1873). Bain (1863) introspects the origins of adverbs and their degrees of comparison, admitting that a limited number of adverbs (then, now, never, etc.) cannot be compared from the nature, whereas the rest form degrees of comparison analytically or take synthetic forms 'er/est', providing the examples, like 'latelylatelier', 'gently -gentlier', 'hardly -hardlier', etc. This theory is proved by Brown (1851), who mentions that in the 19 th century there were about 2600 adverbs, four fifths of which ended in '-ly'. The research on etymology of adverbs and their degrees of comparison contributes to the division into 'declinable' and 'indeclinable' categories. According to Fowler (1855), Clark (1862), Nesfield (1898), and others, adverbs belong to indeclinable, whereas Becker (1845) defines them as inflexible parts of speech. A compromise decision is proposed by Meiklejohn (1862) and Bain (1863), who interpret adverbs both as inflected and uninflected words.
This approach provides no ambiguity for prepositions, because they are sustainably determined as indeclinable. In the same way, the common definition of the category undergoes no significant changes and describes prep-ositions as words used to show the relation between a following noun or pronoun and some other word (see Bullions, 1859;Kerl, 1867;Speers, 1879). Grammarians, however, do not fully neglect the category and specify the possibility to use not only nouns and pronouns after prepositions, but something that can function as substantives, e.g., nouns, pronouns, adverbs, adjectives, infinitives, participles, clauses, etc. (see Currey, 1856; Bain, 1872; Quackenbos, 1873; Rigdon, 1890). Moreover, some other tendencies are developed in linguistics. Firstly, grammarians introduce such terms as a 'regimen' (see Covell, 1853; Bain, 1872), a 'subsequent' (see Bullions, 1859; Brown, 1879), a 'complement' (see Yates, 1873;Powell & Connolly, 1899), or an 'object' (see Holbrook, 1873;Rigdon, 1890), to define a word governed by a preposition, and an 'antecedent' (see Bullions, 1859; Holbrook, 1873), for a word preceding a preposition. Secondly, grammarians try to look into the etymology and origins of the class. They apply the same principles as before and explain the category of prepositions on the basis of the name. Nevertheless, linguists refer not to Latin, like they did earlier, but to the Old English language, emphasizing their original position before verbs and primitive function to connect all sentences back to the verb (see Mason, 1858;Barrett, 1861;Morris, 1880;Daniel, 1881). This has obviously been altered under the influence of Latin, and owing to the language evolution, prepositions occupied their position before nouns and pronouns. At the same time, the idea of probable omission of the substantives becomes widespread, assuming that nouns or pronouns are understood or reconstructed.
In the second half of the 19 th century, the grammarians continue searching for some new ways of representing prepositions, predominantly interpreting them in terms of phrases (combinations of prepositions and their complements) that serve as adjectival or adverbial modifiers (see Mugan and Collins, 1890;Maxwell, 1891;Lyte, 1899). Such an approach shows that the linguistic studies partially leave the level of independent lexical units and shift to the syntactical level of clauses and sentences.
This tendency is observed within the category of conjunctions as well, the main function of which is to connect either 'words and/or sentences' (see Brown, 1851; Barrett, 1861; Maxwell, 1891), or 'words, phrases, clauses, sentences' (see Covell, 1853; Meiklejohn, 1891). Another factor, which finally presupposes the leading character of the syntactic approach, is the division of conjunctions into subcategories. In the early 19 th century, the division into coordinating and subordinating conjunctions was sporadic, if not unique, cf. Murphy (1800). In the second half of the 19 th century, this approach becomes predominant, but the terminology is not normalized, for instance, Mason There are several individual approaches, according to which grammarians distinguish syntactic (function), semantic (meaning), and morphological (form) subdivisions as equal and simultaneous (see Holbrook, 1873;Daniel, 1881). This attests that the focus alters from the semantics of lexical units and concentrates on functional perspective of syntactic units in the language, cf., Osborne (2019). It also means that studying the category of conjunctions, linguists try to apply the functional approach, according to which conjunctions connect not words, parts of sentences, or sentences, but names of things, qualities, actions and beings, modes of action and beings, thoughts, ideas, judgments, and even statements or affirmations (see Barnes, 1854; Bain, 1872; Fleay, 1884; Mead, 1896).
Despite clear syntactic differences between the categories of conjunctions, adverbs, and prepositions, as "the conjunction differs from the preposition in not having an objective after it, from the relative -in joining prepositions and forming no part of either; from the adverb in that it cannot be moved without destroying the sense" (Davies, 1877, p. 116), the problem of categories overlapping still remains of great interest. Firstly, prepositions and conjunctions, as well as adverbs and some other parts of speech, belong to the class of connectives (see Brown, 1851; Barrett, 1861; Bain, 1872). Secondly, the grammarians mention the ability of the same lexical units to function as different parts of speech; for instance, Bain (1872) speculates that a number of conjunctions may have an adverbial character or function as prepositions.
Analysing the category of particles, it is worth mentioning that it remains absolutely ambiguous and undefined. According to the traditional approach, particles include adverbs, prepositions, and conjunctions (see Clark, 1862; Maetzner, 1874; Gostwick, 1878). Discussing possible overlapping of the categories, Seath (1899) offers a new term 'introductory prepositional particles', which covers prepositions and adverbs. Bailey (1855) and Wood (1857) add interjections to the list and define particles as an indeclinable part of speech. Lowres (1863) refers to the category of particles all small words known by the names of prepositions, conjunctions, and articles. Another group of grammarians draws an analogy between particles and prepositions, prefixes of prepositional origin, or affixes in general (see Clarke, 1852; Hiley, 1853; Brewer, 1869; Fleay, 1884). Somewhat simplified approach is discussed by Latham (1870), who states that particles are unsusceptible of inflections and comprise interjections, direct categorical affirmatives, direct categorical negatives, absolute conjunctions, absolute prepositions, adverbs unsusceptible of degrees of comparison, inseparable prefixes. All these approaches testify the absence of unanimity as to structure, functions, and etymology of prepositions, adverbs, conjunctions, and particles, which arises due to perplexity of the notions. And very often this perplexity stimulates the use of oversimplified approaches, when just one element from the 'form-meaning-function' triad moves to the fore in PoS identification.
Overviewing the late 19 th century, special attention should be given to the ideas suggested by Sweet (1892), which do not lay the foundation for other theories and classifications, but are determinative in studying functional transposition from the perspective of the etymological approach, which is being developed. On a par with simple, compound and group-conjunctions, Sweet (1892) distinguishes primary conjunctions which "are used as conjunctions only, such as 'and', 'or'. Some are also prepositions, such as 'for', 'since'. As the prepositional use of these words is the original one, they may be regarded as secondary conjunctions" (p. 140). Validating the necessity to study parts of speech within the triad 'form-meaning-function', Sweet (1892) suggests the following subcategories according to the 'function': word-connecting, sentence-connecting, and independent adverbs; according to the 'meaning': affirmative/copulative, alternative, negative, adversative, concessive, hypothetical, temporal, and causal.
From then on, linguists try to concentrate on the 'form-meaning-function' approach and attempt to combine allin-one. Along with that, the 'etymological component', which, according to Sweet (1892), is a part of the 'form', becomes non-demanded, as the entire attention in studying the 'form' is paid to morphological markers. Disputing with Sweet (1892), I argue that distinguishing the 'etymological component' as a part of morphological form is unreasonable. The lexical unit may appear in the language both in a single and compound form and, at the same time, it can be designated either as primary or secondary. Therefore, interrelation between the primary/ secondary form and primary/secondary function, as well as meaning, is not univocal and undisputable. That is why I substantiate the necessity to separate the 'etymological component', or, in other words, primary use of a word in language, from the 'form' and designate it as an individual element on a par with the form, function, and meaning. It helps to provide complex description of lexical units, introducing diachronic perspective to the synchronic one, represented by the 'form-meaning-function' approach.
In the early 18 th century, the study of the Latin parts of speech system dominates in the English grammar and this predetermines the lack of further unique developments within it. Following the tradition, the majority of grammarians apply not only the 8 PoS classification from the Priscianic grammar but also the definitions found in it. Due to this, an adverb is interpreted as a word joined to a verb, another adverb or a noun. The others try and justify their disagreements, refuting the ability of adverbs to combine with anything of substantival nature. As a result, the category of adverbs is composed of lexical units which denote from 5 to 20 different significations, e.g., action, manner, order, time, place, distance, relation, quality, quantity, comparison, doubt, affirmation, negation, demonstration, interrogation, etc. Later rearrangement of the Latin system and refinement of the English one reject the ability of adverbs to combine with substantives, however, all miscellaneous lexical units still remain within the category of adverbs, making it ambiguous and diverse. Prepositions fall under the influence of the Latin grammar as well, being interpreted as the category which serves to connect other words with one another and show relation between them. Nevertheless, the divergences between the Latin and English languages make it necessary to reject the notion of cases and specify the Conclusion classes of words connected by prepositions -substantives. It distinguishes prepositions from adverbs, whereas the ability to connect different lexical units bridges the gap between them and conjunctions. The latter are defined either as a part of speech, words, or particles, whose service is to connect words, sentences, and/or even meanings. Thus, the category of conjunctions can be divided into a wide range of subcategories -from 2 to 14. Conjunctions are not the only words identified as particles, which include various lexical units, like prepositions, adverbs, numerals, all short words, and even a number of prefixes, depending on the linguists' approaches.
In the late 18 th century, the English grammatical tradition starts its gradual remodeling in order to correspond to the actual patterns and paradigms. This is fully reflected in the grammar books of the first half of the 19 th century in which the major trends remain unchanged, but new approaches appear. Adverbs completely lose the ability to modify substantives and are defined as a part of speech, joined to a verb, an adjective and sometimes to another adverb to express some quality or circumstance respecting it. Classes of adverbs predominantly remain unchanged and their multiplicity make linguists interpret adverbs as corruptions of other words or abbreviations of phrases and sentences, used to comprise in one word what otherwise would require several words. This leads to another important conclusion according to which adverbs are defined as the secondary part of speech and, therefore, cannot appear in the language on a par with the primitive/primary word classes. In contrast to the category of adverbs, where even the number of classes is not strictly specified, the representatives of the category of prepositions come into the spotlight, being fully enumerated almost by all grammarians, and are immediately transformed into the closed word class. As many units morphologically overlap with adverbs and conjunctions, the phenomenon of cases substituted by prepositions becomes widely discussed in order to differentiate the aforementioned parts of speech. In fact, at this period, the study of prepositions shifts to the syntactic level with the notion of stranded preposition being officially registered. It attests formalization of the category of prepositions in grammar. Similar shift towards the syntactic approach is also observed within the category of conjunctions, which is previously analyzed either semantically or morphologically. The approach becomes predominant in linguistics and finds its main reflection in a new division into the subcategories; however, the semantic and morphological classifications are in use as well. It results into a unique approach, when the category of conjunctions is divided into subcategories on the basis of the syntactic factor, while the following division of the subcategories into types is carried out in line with the semantic factor. Nevertheless, none of the approaches or their combinations allows grammarians to formalize the definition of the category and the conjunctions are interpreted either as the part of speech, simple words, or particles. Another factor that adds to ambiguity is the idea that conjunctions may join sentences, elements of sentences, etc. which are not 'physically' represented in discourse. This again approaches them to the category of prepositions whose complement can be hypothetical as well. The development of particles comes to a deadlock, as their category comprehends articles, pronouns, prepositions, conjunctions, adverbs, broken words, contractions, inseparable prepositions, and interjections in various combinations, depending on the linguists' perspective. Thus, among the four categories under study only prepositions and conjunctions partially follow the 'form-meaning-function' approach, while adverbs and particles cannot even be fully described in terms of one of them.
In the second half of the 19 th century, the ambiguous nature of adverbs amplifies the idea that the category may include any word which does not fall under other well-defined PoS. The adverb is still identified as a word used to modify the meaning of a verb, an adjective, another adverb, however, the study of the category in general shifts to another level, because the linguists start analyzing adverbs as modifiers of phrases, clauses, sentences, propositions, and ideas. In compliance with earlier research grammarians continue describing adverbs as substitutions for phrases, clauses, sentences, etc. As a result, adverbs are identified as the representatives of a secondary word class. General development of historical linguistics stimulates the study of etymology of adverbs, intended to give an insight into their nature. It contributes to the distinction of declinable and indeclinable adverbs, but it does not help to distinguish the lexical items which morphologically overlap with prepositions. The latter category is studied exclusively in the frame of indeclinable PoS and retains all theoretical achievements of the previous research. As the syntactic approach predominates in linguistics and the category of prepositions was in general formalized, grammarians focus on the relations between prepositions and words they govern.
It resulted in a number of new terms, like regimen, complement, subsequent, or object, which are applied to designate possible words to the right of prepositions. Moreover, prepositions start to be regularly defined as a part of a phrase, which serve as an adjectival or adverbial modifier. Another significant trend, registered at the period, is the physical omission of prepositional complements, i.e. nouns or pronouns, if they are understood or reconstructed from the sentence. These developments attest that the syntactic approach takes the upper hand in the PoS theory. The same tendency is observed within the category of conjunctions, which are described as units connecting not just words and/or sentences, but syntactic elements like subjects, objects, phrases, clauses, complex and compound sentences, etc. The syntactic approach to their subdivision becomes predominant, though the terminology is not established yet. The refinement of the category of conjunctions discloses another layer of overlapping between adverbs, prepositions, conjunctions and some other parts of speech and contributes to distinguishing the class of connectives, which comprises the aforementioned categories and even more. Furthermore, this approach adds to the notion of particles, giving another common ground to merge prepositions, adverbs, and conjunctions into one category. Grammarians, however, do not limit particles to the three categories, adding to them affixes, prefixes, articles, interjections, etc., i.e. transforming them into the 'container', where all ambiguous, overlapping, and undefined words and classes are stored. And this, in fact, resembles the primary approach to adverbs, according to which "every word when a grammarian knows not what to make of it, he calls an adverb" (Cramp, 1838, p. 148). Thus, if the category of adverbs required several centuries to become more or less outlined and registered in the language, not taking into account numerous overlapping with other parts of speech, it seems highly improbable that the category of particles will follow the same scenario and become an independent part of speech, when the PoS system is formalized and institutionalized in the grammar tradition of the 21 st century.
Therefore, it becomes apparent that final theoretical distinguishing between adverbs, conjunctions, prepositions, and particles is not possible on the basis of the traditional triad 'form-meaning-function', which does not provide a comprehensive interpretation of the PoS theory, and leads to the temporary shutdown of complex research in this sphere. To address this, I suggest involving practical etymological research on the aforementioned parts of speech, which will predetermine broad synchronic-diachronic analysis, develop a primary classification of parts of speech, describe shifts and transpositions within the parts of speech, and explain divergences which are distinguished at different stages of the language development.
The study lays the foundation for the research on overlapping between the categories of prepositions, adverbs, conjunctions, and particles in the realm of cognitive grammar, universal grammar, construction grammar, and other theories and approaches, which play a key role in modern linguistics.