There’s a pretty fluid discussion evolving about the optimal length of a book series over at Science Fiction & Fantasy Chronicles, a website for authors in those genres.

On one side is the argument that readers grow tired of a series after about six books, so it’s in an author’s best business interests to aim for six-book series. The other side argues that if you write from passion and not from monetary targeting, readers will stay with you for however long.

Interestingly, both sides reference Sir Terry Pratchett’s Discworld series. There are forty-one core novels of the series (and with add-on books like atlases and ’Science of Discworld’ etc, the number gets over sixty), but the series doesn’t always follow the same characters, and you can break it down into subsets based on those characters.

If you look at the subsets, Rincewind has six novels, as do the witches, Tiffany Aching, and the industrial revolution. Death only has five novels (yes, he’s a character and he evolves, emotionally), while the city watch (or Sam Vines in particular) has eight novels.

Frank Herbert’s Dune series started as a trilogy, that he later expanded to six titles (then his son took over writing them, and yeah, it gets complicated, don’t ask).

Further supporting the six-novel target is the fact that Amazon’s A+ Content system for KDP (which helps authors promote a series) is set to a maximum of six titles. If anyone knows readers’ habits, surely it’s Amazon?

Looking beyond science fiction, but to adjacent genres such as action, military adventure, etc., we find that to date Lee Child has written thirty Jack Reacher novels. Tom Clancy’s Jack Ryan series is twenty-one novels, with tied-in titles taking it to over forty.

As both a reader and a writer, where do I fall in this debate? As a reader, I’ve read almost all* of the core Discworld novels, but I do tend to re-read only subsets (usually not Rincewind). When I re-read Dune, I tend to stay in the original trilogy, or occasionally will read the fourth book, God Emperor of Dune.

As a writer, I definitely don’t write with an eye towards monetizing.

I originally thought the Deacon Carver Chronicles would be a seven-book series, each exploring one of the seven members of the IU. Now, as the story has evolved, most of it takes part after the fall of the IU, and we only go to one member world. As the story has evolved, it’s also contracted to five (maybe even four) books.

Tau Ceti is a standalone, but it has sequel potential. I know what the next two stories would be if they become compelling enough to write.

A Godless Man is a completely standalone story, but what’s revealed in it would allow for an unlimited number of equally standalone stories with the thinnest of linkages. I don’t feel compelled to explore those.

If the six-book theory is correct, I may not do well finding an audience.

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Footnote:
There are two Discworld books I haven’t read, the last Rincewind one because I was tired of the character, and the last Tiffany Aching one because I know Sir Terry was struggling with a fatal illness, and that book will always be the very last Discworld book.