dents of English should be taught how to choose stylistically suitable words for each particular speech situation.
So far as colloquialisms are concerned, most students' mistakes originate from the ambiguousness of the term itself. Some students misunderstand the term "colloquial" and accept it as a recommendation for wide usage (obviously mistaking "colloquial" for "conversational"). This misconception may lead to most embarrassing errors unless it is taken care of in the early stages of language study.
As soon as the first words marked "colloquial" appear in the students' functional vocabulary, it should be explained to them that the marker "colloquial" (as, indeed, any other stylistic marker) is not a recommendation for unlimited usage but, on the contrary, a sign of restricted usage. It is most important that the teacher should carefully describe the typical situations to which colloquialisms are restricted and warn the students against using them under formal circumstances or in their compositions and reports.
Literary colloquial words should not only be included in the students' functional and recognition vocabularies, but also presented and drilled in suitable contexts and situations, mainly in dialogues. It is important that students should be trained to associate these words with informal, relaxed situations.
Much has been written on the subject of slang that is contradictory and at the same time very interesting.
The Oxford English Dictionary defines slang as "language of a highly colloquial style, considered as below the level of standard educated speech, and consisting either of new words or of current words employed in some special sense."