I love the short story and I love the novel, but what about the in-between sizes? What about stories too long to be short? Or not long enough to be novel? Some of my favourite books, running to 60 or 100 pages, are classified (or could be) as novellas. I think of Ian McEwan's dark The Comfort of Strangers, or the wonderfully grotesque Ballad of the Sad Cafe. There's Death in Venice, Heart of Darkness, and Goodbye, Columbus.

One virtue of a novella is that it's compact enough to be read at a single sitting, two to four hours depending on your reading speed. Enough time to savour its length without having your reading experience broken up into fragments. I also like how the novella offers a focused, highly concentrated read, without the breadth and moving parts of its weightier sibling the novel.

It's hard to generalize, but novellas seem to chart the different stages of a character's obsession or decline. Things don't happen all at once, as they do in a short story (after which nothing is ever the same again). Novellas work in increments, but nonetheless relentlessly.

Can I claim The Dead as a novella? And the Death of Ivan Ilych. And Chekhov's wonderful Lady with a Lapdog, not to mention The Duel.

All praise the slim novella (and all other in-between sizes). One size, or two, does not fit all. And one cheerful feature of the digital revolution seems to be its promise that size will no longer matter when it comes to good reading.