Defining the preposition, linguists usually point out three main proper­ties: 1) the preposition is a functional part of speech, i.e. a preposition cannot perform an independent syntactic function; 2) the preposition is a word ex­pressing subordinate relations between lexical parts of speech; 3) the preposition is a word with an obligatory pre-nounal position: it may follow almost any part of speech, but it must precede a noun or its syntactic equivalent.

Prepositions, like functional parts of speech in general, are a compli­cated and controversial phenomenon. On the one hand, they are discrete, separate words; on the other hand, these are words that exist only together with others. The English preposition presents the following issues for lin­guistic analysis.

One and the same concept may be expressed by means of both a lexi­cal word and a preposition, e.g. purpose and for. Some linguists, in order to reveal the difference between these two ways of expression, deny any lexical meaning, peculiar to prepositions. Their opponents claim that lexical meaning of a preposition is subordinated to its grammatical meaning. This approach is not quite correct, since grammatical meaning of prepositions is to indicate subordinating relation. The relation of purpose is among others, such as location, direction, source, instrument, etc.

Each of the meanings is expressed by a number of prepositions that may have a variety of concrete meanings (take, for example, the meaning of location indicated by the prep­ositions in, on, under, over, around, at, by). These concrete meanings are registered in dictionaries, which gives the ground to suppose that the prepo­sition does have a specific lexical meaning. The specificity of this meaning lies in that it is expressed by a preposition only in combinations with lexical words. Compare, for instance, the answer to the question Where shall I put the gloves? that may be On/Under/By the box. The answer On/Under/By is impossible. These observations lead us to believe that the preposition is deprived of the nomination ability: it does not name a relation, it only points this relation out.

The preposition marks a relation between words, and therefore it may be expected to function between the two words in order to relate them to each other. This expectation is not, however, always met. The most widespread case, with the left component absent, is quite frequent in titles (Across the river and into the trees) or in sentences where the subject is expressed by a prepositional phrase (In the drawer is where you should put the money). In the latter sentence, though the preposition in is semantically related with the verb put, syntactically they are separated. It should be noted that the left component is always present – explicitly or implicitly – and it is the left component that determines the choice of a preposition.

Prepositions, like all functional words, do not have any morphological properties. The majority of prepositions are root words that appeared in Old English or even earlier. Though one might expect prepositions to be a closed word class, new prepositions do appear. New formations are rare and the process of formation takes much time. A preposition is, as a rule, formed through desemantization of some morphological forms, for example, parti­ciples: considering, during.

Phonetically, a number of prepositions are absolutely identical with ad­verbs and so-called postpositives. Jespersen believed that these should be treated as two different uses of one and the same linguistic unit. However, since this linguist did not differentiate lexical and functional words, this interpretation might hardly be relevant in terms of our analysis. The ma­jority of modern scholars argue that these cases are examples of linguistic homonymy, i.e. that the words, identical in their phonetic form, belong to different parts of speech.

The words before, after and since may be an example of a stumbling-block issue, i.e. an example of confused correlation between the preposition and other parts of speech. The majority of linguists believe that, depend­ing on the distribution, each of these phonetic forms may belong to three parts of speech – the preposition (Jack always arrives after his wife), the conjunction (Jack arrived after his wife picked up the kids), and the adverb (Jack came shyly after). The adverb is easily recognizable, for it does not express any relation but stands on its own and functions as an independ­ent sentence part.

It is not so simple to interpret the difference between the preposition and the conjunction. The term “homonymy” in its conventional sense is not applicable here, since conventional homonyms are phonetically identical but semantically different. In this particular case, functional words, introducing either a word or a subordinate clause, have similar temporal meanings. Meanwhile, in the first sentence after preserves similarity with prepositions, whereas in the second sentence it resembles conjunctions.