One of the things that's often recommended to neophyte writers of novels is to have one scene per chapter. And someone then asks "What's a scene?" and someone else "How long should a chapter be?" And they're right that the two things are interrelated, but I don't think one-scene-per-chapter is necessarily the best solution. And the length any chapter "ought" to be is actually determined by what you think a chapter is. So, what's going on?
We all know what a scene is in a play, of course... or do we? English drama packs multiple comings and goings into a single scene, and traditionally a new scene expresses a break in time or space. French drama starts a new scene each time a character enters, which seems odd to us, though I enjoy the way it also smells of M Molière's rehearsal call sheet. But the French tradition says something important too: when a new character comes in, the dynamics of character-in-action are, by definition, changed; a new unit of action, if you like, has started.
Of course, fiction integrates dramatic prose with narrative prose and (thanks to free indirect discourse) blurs the distinction between them. So, unlike visual drama (film, plays), in fiction the distinction between action shown "on stage" in real time, and other ways of telling a story, is elided or even eliminated (and it is to some extent in radio drama, too). But I'd suggest that understanding change is still the key, and so one way of thinking about scenes is as units of change. Where, when you're starting a scene, are you hoping to end up? What will have happened by the end? Will you, in the writing, discover that the change isn't what you expected? As I was exploring in Clothes and Food and Dropping Presents, you may do that discovering by imagining then writing externals - what people do, what they say, what they eat or sing or hit - and by that means discover what's "really" going on in this unit of inter-action between your characters, and their environment. Or you may discover by imagining then writing internals - how each feels and thinks, what they want or need - and letting what you've imagined shape how they act. But either way, by the end, a unit of character(s)-in-(inter)action has become a unit of change.
And one-scene-per-chapter? It's a nice, simple and therefore strong way of expressing/embodying that basic unit, so I'd never say never. But I do think it's missing an opportunity, for two reasons.
First, one of the big differences between short fiction and novels is that a novel needs big structures of change, as well as small ones, with a sense of big change (which is what the hook/elevator pitch is always implying) to carry us through the length of the novel: a change which is built of smaller changes. A chapter is the main unit of structure that's available to you as a novelist, and if each smallish change is a chapter, how do you express/embody the main, big changes? You can have Parts, but with only three, say, they may be too big. To go back to the analogy I was making in Building the Bridge, is the bridge you're building made of hundreds of identical legs, low and flat, trotting across to the far bank which is the end of your story? Or is it a series of piers and arches, perhaps of different widths and heights, perhaps rising to a crown and down again, which embody the big, stretching strides? There is always the Part, as the biggest unit of organisation, but frankly I often forget about them when I'm reading a book: I think most of us feel that the chapter is the basic unit, and happily "read" section-breaks or switches of narrator, say, as joints in a larger whole. So why not make the most of the reader's willingness to "get" the bigger architecture?
And, second, I think by making a single scene your biggest unit of action you're at risk of thinking that such units are the only thing your novel is built of. Whereas, to extend the Orient Express metaphor I used a while ago, I think it can be extremely useful to think of a novel as a train. If the major scenes are the carriages, and you write them in full, showy, almost-real-time glory, then the couplings are also crucial: not just the big steel hooks and chains, but the electrics, communications, brakes, platforms, doors and so on. You can't have one without the other and any railway buff knows that the engineering of the couplings is as fascinating and crucial as any other part of the train. Once you've mastered really effective Telling, as well as Showing, you'll be able to make those couplings, too, an active part of how you tell your story. And if you're integrating them into the storytelling train, then your unit of storytelling is no longer a single scene, but a complex of smaller and larger units of character-in-action which make up a bigger unit. Shall we call that a chapter?