Obsolete words which you might need to understand long-dead writers.

( perdie, sapid ) Technical vocabulary which only a small sector of the population would understand.

( perchloric, perdendo ) Regional vocabulary which is only used in one country or region.

( sapples, gossoon ) Words which, although they exist, have never been part of common speech.

( conglobulate, manducate ) Colloquial or slang words which are ephemeral.

( cosh, peeler ) The words in brackets are examples of each category; if you want to find out what they mean, look them up in Chambers English Dictionary. It won't do you much good, though; you will quite possibly never see them again, and will certainly not want to use them.

You will have noticed that there is only one category of words for which I have not given examples. The reason is that every other word in this article should belong to this category; I say ''should'' because everybody has his own idiosyncrasies of vocabulary, and I am not an exception.

The object of writing is to convey a message of some sort to a reader. That reader may be one of a specialised group, in which case you may be able to use specialised vocabulary, but in most cases you will be writing for one or more of that amorphous group known collectively as ''the general reader''.

I was once given the task of reviewing a book by an American academic, a specialist in his field, who was writing for the general public to read. By the middle of the second page I was lost; the structures were so tortuous, the syntax so entangled, the vocabulary so unnecessarily obscure, that the writer had totally failed to communicate whatever it was he wanted to say. I never found out.

Clearly this writer had failed in the primary purpose of his writing. Never mind beauty of style and elegance of expression; never mind that elusive quality which our ancestors called ''wit'' (Pope described it as ''what oft was said, but ne'er so well expressed''). A writer must communicate to his desired audience, or he has wasted his time.

This means that vocabulary must be straightforward, and words must be chosen for clarity rather than to display learning; words, indeed, should be chosen, and should not just spill out as it were by accident.

This is not the same thing as saying that you should always use simple, common words. I have used a few in this article which are not particularly common but which, I hope, convey just the right meaning for what I wanted to say. Here are two of them, andthe reasons why I chose them.

Idiosyncrasies This means the individual personal characteristics of a person's actions or temperament, which are unique to himself. By derivation it means an individual mixing together, one's own personal blend of ideas. The word is common enough to be understood by any educated person, and is the only word which has that precise meaning.

Tortuous This means full of windings, far from straightforward. It contains the same root as TORMENT and TORTURE, and therefore neatly hints at the fact that I didn't find it particularly pleasant to read.

What you like, what I like, what a third reader likes, will not necessarily coincide, nor should they, because this piece of writing is mine, and it is up to me how I write it. What I must do, however, is to ensure that it is clear and unambiguous, and that what I want to say is said in such a way that the targeted reader can understand it.

Don't fill your writing, essays or letters or whatever you have to write, with sesquipedalian verbiage; your readers will not understand it, and it will not match the rest of your style.

Those two long words, by the way, mean ''long words'', and most of the people reading this article didn't understand them! What is important is that it is a fault of style to use these words, a fault which I committed deliberately in order to demonstrate to you exactly how a reader reacts. It does not show that I am cleverer than you are; it may show that I know more words, but this is of no use at all if I do not know how to use them.

So my first point today is, ''Use plain words''. My second is, ''Use words which you can understand''.

Language is a precision tool; it is like an arrow aimed at the bull's-eye, not like the pellets blasted from a shotgun. The latter may make more noise and cover a wider area, but they will have less effect at anything but the closest range than the more delicate arrow.

The following, a quotation from the English poet Keats, is a verbal arrow which hits the bull's-eye.

''A thing of beauty is a joy for ever.'' You could not find simpler words; they must all be in the primary school syllabus. You could not even find simpler syntax or more elementary grammar. The meaning, however, is absolutely clear; and I challenge anybody to say the same thing in a more effective way. I can't.

BROMIDE No. 102581