Conjunctions are functional words that connect separate words, word combinations, clauses or sentences and in doing so mark the relations of coordination and subordinatioh.jConsequently, the grammatical meaning of conjunctions is similar to that of prepositions: conjunctions mark grammati­cal relations but these relations are even more abstract than those indicated by prepositions.

Conjunctions form a part of speech genetically related with words of other parts of speech. A number of conjunctions are derived from adverbs or prepositional phrases as well as from forms of lexical words, e.g. provided, supposing, seeing.

Moreover, linguists claim that some nouns, in fact, func­tion as conjunctions undergoing the process of partial desemantization. These nouns are the moment, the instant, the way and the adverb once: I didn’t like him the moment we were introduced to each other; I don’t like the way he works this month; Once you are let down, you stop trusting people. As a re­sult, the problem of grammatical homonymy of conjunctions and otner parts of speech is one of the most controversial and important. Some conjunc­tions have homonyms among adverbs, prepositions, particles, etc. We have already considered the linguistic unit after. Another example is but that may function not only as a coordinating conjunction (slow but efficient), but also as a preposition (nobody but him) or a particle (saw him but yesterday).

One of the most controversial cases is the use of the comparative like. It seems quite acceptable to believe that distribution plays the crucial part for classification. Depending on the distribution, like is treated either as a preposition (It s not like what we hoped for; He looked like a stranger), or as a conjunction (Try to live like you used to), or sometimes as an adjective (They are as like as two peas) or a noun (We shall not see his like again). 

Clearly, defining the conjunction, one faces difficulties in drawing a fast and ready borderline between the conjunction and the preposition. A rela­tion, marked by a subordinating conjunction, resembles much that of the preposition. As a result, though the former is mainly used in the complex sentence, there are exceptions such as if possible, when at a loss, in which the subordinating conjunction connects separate lexical words or word com­binations.

As a rule, this function is performed by prepositions or coordinat­ing conjunctions. These observations give rise to doubts whether is it justi­fied to differentiate between these two parts of speech. Obviously, lexical meanings of functional parts of speech may hardly be separated from gram­matical relations marked by these words; it is for this reason that combin-ability of functional words and their distribution determine to which part of speech these words should be referred. Consequently, all these disputable cases should be regarded as cases of homonymy.