Plot of the story
A character with a problem.
Every story is about a character trying to deal with some sort of difficulty. Characters who have happy lives, who are ********************* with their lot, and who have achieved their goals are not good fodder for fiction. The people we read about are people in trouble.
The central problem.
Most genre stories can be thought of as revolving around some central problem, or problems. The central problem(s) can be considered to be, in some sense, what the story is "about." Will the mystery be solved? Will the protagonist survive? Will the rebellion succeed?
Begin with a crisis...
Whatever the length you're dealing with, short story or novel, you want to begin with a character in crisis. The reader should find characters in difficulty within the first chapter, the first page, and ideally, the first paragraph. Structurally, it may not be possible to have the story's main problem begin on the first page, but every story should begin with some problem, often with the first line.
...end with a resolution.
If the story is organized around a single central problem, it ends naturally when you've resolved that problem. If the story deals with a series or complex of problems, it ends when the last problem is dealt with, or when all the problems identified as most important are solved. A story can persist as long as there are problems to deal with.
What makes a Story Science Fiction?
The central problem and its con************.
A story is SF when the central problem dealt with by the characters is a science-fictional idea, or when the central problem is resolved by science-fictional means. This means that if the SF elements are removed from the story, either the central problem, or its resolution, will cease to exist, causing the story to collapse.
"If it's a western, it ain't SF."
It is by no means a consensus, but there is a large body of thought that says that a story has to have more than an SF setting to be SF. In other words, if the characters and plot can be successfully transplanted to a non-SF setting, it isn't really SF. If all you're doing is setting a western in a post-apocalyptic setting, you're probably better of simply writing a western.
What is Plot?
Cause and effect. Stimulus and response.
Plot is the structure of events within a story and the causal relationship between them. There is no plot without causality. "Captain Stronghead piloted his spacecraft to Proxima Centauri," is an event with no plot. "Captain Stronghead piloted his spacecraft to Proxima Centauri in order to escape the despotic regime on Earth," has the beginning of a plot.
The causal chain.
The plot of a story is a chain of events, each event the result of some prior events, and the cause of some subsequent events. The plot of a story will extend beyond the bounds of the story itself.
How does Plot develop?
Things get worse.
Up until the resolution of the story's central problem (or up until the resolution of the most dire of the story's problems) the situation should steadily get worse— or more difficult— for the protagonist. Even if the protagonist's situation objectively improves, which happens in many "rags to riches" stories, the forces arrayed against the character should grow comparably in magnitude. If the protagonist picks up a bat, the antagonist should pick up a knife. If the protagonist picks up a knife, the antagonist should pick up a gun.
The active protagonist.
Not only should the difficulties increase steadily until the climatic moment when the central problem(s) are resolved, but the difficulties should be increased as a result of positive action by the protagonist. Your characters should not sit by and watch the world fall apart, doing nothing. The characters in your story should have an active part in destroying the world around them. Every attempt to solve a problem should make the problem worse, or create a new, more tenacious, problem. Problems can worsen without interference by the characters, but the characters should always be doing something about the problem(s), and what the characters do should worsen— or at the very least, change— the problem(s) they are trying to solve.
Complicate, Complicate, Complicate
Things getting worse is not a matter of simply increasing the magnitude of the problem. (Discovery of the fact that the asteroid about to hit Earth is 1500km across rather than 500km across.) Things getting worse in a story sense means a proliferation of new problems rippling from the old. (The realization that the technical failures in the escape spacecraft are the result of sabotage.) Complication means that the problem the characters were trying to solve is not quite the same as the problem they actually face.
Character as Plot.
Motivations, desires, goals.
Since plot is not just event, but the casual relationships between events, plot can not be isolated from character. Characters do things for reasons, and those reasons form an indispensable element of plot. Every character in a story desires things to varying degrees, and has personal goals in mind, some of which may not have anything to do with the central problems of a story. Whatever these desires and goals are, they form the basis for your character's motivation to act. You want the characters within your story to be acting from these desires and goals, and not from the external demands of the plot.
Conflict with others.
A great source of difficulty for your characters is when their personal drives are at odds with the central problem in the story. A man whose highest ambition in life is to live a quiet life and raise a family is going to be torn if he is drafted into an army in the middle of a civil war. He will act differently than a man who has a hedonistic lifestyle and whose desire is simply to make each moment as pleasurable and exciting as possible. Placing these two characters together in a combat situation and they will start arguing immediately.
Conflict with self.
Perhaps the greatest source of difficulty for your characters, and the most emotionally satisfying when finally resolved, is when the characters have goals and desires that are mutually exclusive. If both goals are illustrated in the story, and are of comparable importance to the character, the character will be in a constant state of tension that can border on agony. Consider the family man above. Give him a strong sense of justice that has placed him in this civil war to battle against the atrocities that he's seen the enemy perpetrate (perhaps his family was victimized, driving him into the war.) Give him and the hedonist an opportunity to capture enemy soldiers that've been committing such atrocities. Then have the hedonist begin committing similar atrocities upon the enemy soldiers. What does the protagonist do, is he after justice or revenge?
How does Plot create Suspense?
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