Few people would deny that dictionaries are an effective aid in the language learning progress. Much will depend, however, on the kind of dictionary and how and why it is used. Traditionally, language learners have had recourse to bilingual dictionaries, enabling them to find the mother tongue translation of new words and to find the foreign language equivalent of terms in their native language. In the early years of the Communicative Approach, some methodologists argued against the use of bilingual dictionaries, maintaining that they did more harm than good, mainly by focusing the learner on his or her mother tongue, but also by leading the user to potentially incorrect equivalents.
Certainly, there is some merit in the latter argument. Smaller bilingual dictionaries have a tendency to give translations for all the meanings of a particular word, without giving contextualized examples. They may also imply that words are synonymous when there are nuances in meaning and possible restricted use in collocations. This can lead to confusion and potential errors. This argument does not, however, take account of the common-sense of the learner. Most learners would be able to work out from the context of the piece of language they are looking at that the English word “issue” refers to an edition of a newspaper or magazine rather than to someone’s children.
It is, however, not uncommon for some teachers to forbid the use of bilingual dictionaries in class simply because they believed monolingual dictionaries to be more beneficial to the learner. Monolingual dictionaries specifically aimed at learners of English were comparatively rare until the last twenty years of the 20th century, when a wide range of these dictionaries began to appear. Most of these are an excellent learning tool, giving clear definitions and contextualized examples of how items of language are used. Some dictionaries, the Macmillan English Dictionary for Advanced Learners, for example, also highlight the frequency and usefulness of particular items of vocabulary as well as words which commonly collocate with these items.
The use of the dictionary itself also involves a number of learning strategies from basic reference skills (alphabetical order as the most basic) to advanced reading skills. Indeed, learner training and encouraging the habit of using a monolingual dictionary would seem to be an essential component of current classroom practice. Learner training can focus on a number of aspects, from interpreting symbols and understanding abbreviations (e.g. adj., adv.), understanding phonemic transcriptions and stress marks, to quickly finding a specific meaning of an item of vocabulary.
From the learner's point of view, this may present some difficulties at first. Using a monolingual dictionary requires more effort and commitment than using a bilingual one but, once the practice has become established, it offers substantial rewards. Every time the learner looks up a word, he or she is getting further reading practice in English, seeing words in context, seeing authentic examples of how words are actually used.
From the teacher’s point of view, the most important aspect would seem to be to encourage the use of monolingual dictionaries, perhaps by taking a set into the classroom, getting learners to use them as a matter of course and thereby to become more independent in their language learning, and, finally, to buy a good monolingual dictionary and use it both in class and at home.
This is not to say that bilingual dictionaries should not be used. Better examples of these also contain contextualized examples of the use of items of vocabulary, clear definitions and examples of differences in meaning, as well as phonemic transcriptions as a guide to pronunciation. They also offer the possibility to compare how different concepts are expressed in the mother tongue and the target language. The effective language learner will probably make full use of both types of dictionary.