2. According to the information they provide all linguistic dictionaries fall into two groups: explanatory and specialized.

Explanatory dictionaries present a wide range of data, especially with regard to the semantic aspect of the vocabulary items entered, e.g, the New Oxford Dictionary of English.

Specialized dictionaries deal with lexical units only in relation to some of their characteristics, i. e. only in relation to their etymology, frequency, pronunciation, and usage, e.g. the Longman Pronunciation Dictionary.

3. According to the language of explanations, i.e. whether the information about the items entered given in the same language or in another language, all dictionaries are divided into: monolingual and bilingual.

In monolingual dictionaries the words and the information about them are given in the same language, e.g. the New Shorter Oxford English Dictionary.

Bilingual dictionaries are those that explain words by giving their equivalents in another language, e.g. the English-Russian Phraseological Dictionary (by A.V.Kunin). They may have two principal purposes: reference for translation and guidance for expression. Bilingual dictionaries must provide an adequate translation of every item in the target language and expression in the source language.

4. Dictionaries also fall into diachronic and synchronic with regard to time.

Diachronic (historical) dictionaries reflect the development of the English vocabulary by recording the history of form and meaning for every word registered, e.g. the Oxford English Dictionary.

Synchronic (descriptive) dictionaries are concerned with the present-day meaning and usage of words, e.g. the Advanced Learner's Dictionary of Current English.

The boundary between the mentioned types of dictionaries is, however, not very rigid and the two principles may be blended as, for example, in the Concise Oxford Dictionary. Some synchronic dictionaries are at the same time historical when they represent the state of vocabulary at some past stage of its development.

2 Problems of lexicography

To get maximum efficiency from dictionaries, to secure all the information afforded by them it is useful to have an insight into the experience of lexicographers and some of the main problems underlying their work.

The work at a dictionary consists of the following main stages: the collection of material, the selection of entries and their arrangement, the setting of each entry.

At different stages of his work the lexicographer is confronted with different problems. Some of these refer to any type of dictionary; others are specific of only some or even one type. The most important of the former are:

7. the selection of lexical units for inclusion,

8. their arrangement,

9. the setting of the entries

10. the selection and arrangement (grouping) of word-meanings,

11. the definition of meanings,

12. illustrative material,

7) supplementary material.

1) The selection of lexical units for inclusion

It would be a mistake to think that there are big academic dictionaries that list everything and that the shorter variants are mere quantitative reductions from their basis. In reality only a dictionary of a dead language or a certain historical period of a living language or a word-book presenting the language of some author (called concordance) can be complete as far as the repertory of the lexical units recorded in the preserved texts goes. As to living languages with new texts constantly coming into existence, with an endless number of spoken utterances, no dictionary of reasonable size could possibly register all occasional applications of a lexical unit, nor is it possible to present all really occurring lexical items. There is, for instance, no possibility of recording all the technical terms because they are too numerous and their number increases practically every day (chemical terminology alone is said to consist of more than 400,000 terms). Therefore selection is obviously necessary for all dictionaries.

The choice of lexical units for inclusion in the prospective dictionary is one of the first problems the lexicographer faces. First of all the type of lexical units to be chosen for inclusion is to be decided upon. Then the number of items to be recorded must be determined. Then there is the basic problem of what to select and what to leave out in the dictionary. Which form of the language, spoken or written or both, is the dictionary to reflect? Should the dictionary contain obsolete and archaic units, technical terms, dialectisms, colloquialisms, and so forth?

There is no general reply to any of these questions. The choice among the different possible answers depends upon the type to which the dictionary will belong, the aim the compilers pursue, the prospective user of the dictionary, its size, the linguistic conceptions of the dictionary-makers and some other considerations.

Explanatory and translation dictionaries usually record words and phraseological units, some of them also include affixes as separate entries. Synonym-books, pronouncing, etymological dictionaries and some others deal only with words. Frequency dictionaries differ in the type of units included. Most of them enter graphic units, thus failing to discriminate between homographs (such as back n, back adv, back v) and listing inflected forms of the same words (such as go, gone, going, goes) as separate items; others enter words in accordance with the usual lexicographic practice; still others record morphemes or collocations.

The number of entries is usually reduced at the expense of some definite strata of the vocabulary, such as dialectisms, jargonisms, technical terms, foreign words and the less frequently used words (archaisms, obsolete words, etc.).

The policy settled on depends to a great extent on the aim of the dictionary. As to general explanatory dictionaries, for example, diachronic and synchronic wordbooks differ greatly in their approach to the problem. Since the former are concerned with furnishing an account of the historical development of lexical units, such dictionaries as NED and SOD embrace not only the vocabulary of oral and written English of the present day, together with such technical and scientific words as are most frequently met with, but also a considerable proportion of obsolete, archaic, and dialectal words and uses. Synchronic explanatory dictionaries include mainly common words in ordinary present-day use with only some more important archaic and technical words. Naturally the bigger the dictionary, the larger is the measure of peripheral words, the greater the number of words that are so infrequently used as to be mere museum pieces.

In accordance with the compiler’s aim the units for inclusion are drawn either from other dictionaries or from some reading matter or from the spoken discourse. For example, the corpus from which the word frequencies are derived may be composed of different types of textual material: books of fiction, scientific and technical literature, newspapers and magazines, school textbooks, personal or business letters, interviews, telephone conversations, etc.

Because of the difference between spoken and written language it is to be remembered in dealing with word-books based on printed or written matter that they tend to undervalue the items used more frequently in oral speech and to overweight the purely literary item