I have received a letter from Nancy Bykowski of Bolingbrook, Illinois, which says, in part, "I have noticed the trend in recent years towards trilogies and serial volumes. I enjoy reading a series of books set in the same background, but it can be frustrating when the books do not stand alone...But there are some authors out there that seem to be writing serials so that we will be forced to buy their next book. I believe I read somewhere that the publishers tend to encourage that kind of thinking. So my question to you is, did you write your Foundation trilogy in response to a request from a publisher, or was it simply the result of an idea that was too big for one volume?"

As it happens, I, too, have noticed the tendency for novels to come in clumps these days. (It's true of movies, also. Someday, we will have a motion picture called Rocky XVII Meets Superman XI.)

But why is that? Why are so many writers turning out a series of connected novels?

One very obvious reason is that it makes life simpler for them. Instead of having to invent a new social background for each story, they can make use of one that they have already devised. The writer can thus begin a new novel with a ready-made background and sometimes with ready-made characters. If you're not a writer yourself, you have no idea how much mental agony and psychic wear-and-tear that saves.

Then, too, readers who have enjoyed a book often welcome a return of the same characters and background. As a result, the pressure for a sequel and even for a continuing series is likely to come, at least to begin with, from those readers rather than from the author or publisher.

Publishers naturally welcome any book in which the chance of success and profitability is high. They are always more eager to receive a manuscript from an established writer than from a newcomer because they can usually be sure that the former will be profitable, while the latter always represents a risk.

By similar reasoning publishers would prefer to have an established writer do another book of a popular series than venture in a new direction altogether. The series book is more nearly a sure thing, and publishers are almost as fond of a sure thing as you and I are...

However, are these series of novels written simply to force readers to buy the next book against his will? Of course not. If readers don't like a particular book, they are not likely to buy a sequel. If they like the first three books of a series and find the fourth disappointing, they are less likely to buy the fifth.

In short, a maintained popularity and profitability will tend to keep a series going indefinitely. Non-popularity or declining popularity will bring an end to the series quickly.

As a matter of fact, far from a series of books continuing just to lure reluctant readers into purchasing volumes that they don't really want to read, it is the reverse that is likely to be true. It is the writer, not the reader, who is likely to be victimized. After all, writing a long series of related books can grow awfully tiresome for a writer. He may have sucked the juice out of his characters and background and may long to go in other directions, thus stretching and resting his cramped and aching mind.

The writer therefore quits and goes about his business-and then a storm arises. Readers express loud disappointment and make demands for another book in the series. Publishers, becoming aware of this, and seeing no reason to allow profitability to go glimmering, then proceed to put pressure on the writer, who is often far less enthusiastic about his series than anyone else is-and, in the end, he must write. In that case, anyone who says to him, "You're turning out endless reams of this junk just to con the reader into buying your books," is likely to get a punch in the mouth if the writer is of the violent persuasion, or a sad look if the writer is as gentle and lovable as I am.

I'm talking from personal experience. The first three books of the Foundation series are compilations of separate pieces written for Astounding Science Fiction between 1942 and 1950. They were written at editorial insistence, but, for a while, I was eager to comply.

I had had enough of them after eight years, however, and, in 1950, determined to write no more. I resisted all entreaties for additions to the Foundation series and ignored all threats for thirty-two years! And then, finally, Doubleday began snarling and foaming at the mouth so I agreed to write Foundation's Edge and Foundation and Earth, the fourth and fifth books of the series.

So there you are, Ms. Bykowski. My Foundation series was written, at least in part, as a result of publisher's (and readers') pressures, but they also deal with a theme too large to be contained in one story or one novel, and each portion of the series, whether a short story or a novel, stands on its own.

But is this business of stories and novels in series an invention of science fiction? It certainly is not. It is not even a modern phenomenon. The same pressures that lead to sequelization today were operative in ancient times as well so that sequels and series must surely be as old as writing.

The Iliad had the Odyssey as its sequel, and other Greek writers capitalized on the unparalleled popularity of these two epics by writing other epics concerning events preceding, succeeding, and in between these two (none of which have survived).

The great Greek dramatists tended to write trilogies of plays. Aeschylus built a trilogy around Agamemnon, Sophocles built a trilogy about Oedipus, and so on.

Coming closer to home, Mark Twain wrote Tom Sawyer and when that proved successful, he wrote a sequel, Huckleberry Finn, and when that proved even more successful, he wrote a couple of other tales of Tom and Huck, and when those were not successful, he stopped.

Of course, a series need not concentrate on "continuing the plot." It may consist of a series of independent stories, which, however, share a common background and a continuing character. An enormously successful series of this sort was A. Conan Doyle's Sherlock Holmes stories. So compelling a character did Doyle create in Sherlock Holmes that the public could never get enough of him.

Doyle quickly began to grow tired of writing the stories and, indeed, began to hate Sherlock Holmes who had grown so large in public consciousness as to totally overshadow Doyle himself. In desperation, Doyle killed Sherlock Holmes-and was then forced to bring him back to life. Here is an extreme example of the victimization of an author (though it did make Doyle extremely wealthy). Other mystery novel series featuring a continuing detective (Hercule Poirot, Nero Wolfe, etc.) followed as a matter of course.

When I was young, series of independent stories featuring continuing characters were extremely common. There were the Nick Carter books, the Frank Merriwell books, and others, too. There were magazines which, in each issue, carried a novella featuring some character such as the Shadow, the Spider, Doc Savage, Secret Agent X, Operator S, and so on.

Naturally, science fiction was influenced by such things. During the 1930s and 1940s, Neil R. Jones wrote some twenty stories featuring Professor Jameson and a group of companion robots with human brains; Eando Binder wrote ten stories about another robot, Adam Link; Nelson Bond wrote ten stories about a lovable bumbler named Lancelot Biggs.

However, the first successful series of novels in science fiction were by E. E. Smith. Between 1928 and 1934, he turned out three Skylark novels, and between 1934 and 1947, he turned out five Lensman novels.

In the 1940s, Robert A. Heinlein produced something new in his Future History series. Here the plots seemed independent and were set at widely different times, but they all fit into a consistent historical development of the solar system, so that there were references in stories set later in time to events in stories set earlier in time.

I began another series of this sort with Foundation in 1942. I expanded the background to the galaxy as a whole and proceeded to trace the history methodically from story to story, without jumping about. Later, I tied in my Robot series and my Empire series so that my own future history series now consists of thirteen novels-with others to come, I suppose.

Other series of the Foundation type followed, the most successful being Frank Herbert's Dune series.

In fantasy, the great success was J. R. R. Tolkien's Lord of the Rings trilogy, which inspired a host of imitations. The late JudyLynn del Rey, and her husband, Lester, with their marvelous ability to spot trends, encouraged the writing of novel series and put them out under their publishing imprint of "Del Rey books," so that we now have a virtual inundation of book series.

The fashion may pass, but while it is here, it seems to be bringing us a considerable number of good things to enjoy.