“How do you decide on the form for a particular work? Should it be a short story or a novel?” (Anon, Manila)
This is a question that troubles many writers.
The initial decision is often a practical one. How much time can I spend on this story? Do I have years, or only months? Do I want something book length, or shorter?
Sometimes the material will suggest the form: some stories just need more space. But often you simply make the decision and then find a way of working the story into that shape. Your own interest in the story will give an indication of how many pages it could last.
Embarking on a story is like getting in a car and going somewhere. Sometimes you know where you are going before you get in, sometimes it becomes clear only once you set off. And sometimes you don’t know until you reach the end. If any of those options are not for you, then make sure you do something about it. You are the driver.
At some point in the writing you will need to work out what makes something a novel, or a short story and then engage with it — challenge the form, or at least what you think is the form.