How to write science fiction

You have an idea: a machine that works, a treatment that changes what bodies can do, a discovery that rewrites a law everyone assumed was fixed. The question that decides whether the book is science fiction is not whether the idea could happen. It is whether you follow the idea's consequences further than its first announcement, because consequences are what the genre sells.

The reader contract: the idea and its consequences

Wikipedia's science fiction article describes the genre as speculative fiction that imagines "advanced and futuristic changes in technology, scientific knowledge, or biological systems", often exploring "human responses to the consequences" of the projected changes. Isaac Asimov's definition, quoted in the same article, is the craft version: "that branch of literature which deals with the reaction of human beings to changes in science and technology." David Hartwell's phrase for the genre's appeal names the balance you are striking: "combination of the rational, the believable, with the miraculous."

Read those as a working contract. The reader comes for the idea and stays for what the idea does to people: who gets hurt first, who profits, what an ordinary day looks like once the impossible is ordinary. A technology that changes nobody's choices is set dressing. The discipline is simple to state and hard to keep: for every change you introduce, write down consequences nobody in the story wants, and put at least one of them on the page.

Hard or soft: decide where the rigor goes

The genre's oldest quality-of-attention split is hard versus soft, and the labels are contested; the catalog's hard versus soft science fiction guide covers the history and the caveats in full. The short version: hard science fiction is characterized by "concern for scientific accuracy and logic", aiming to be accurate, credible and rigorous in its use of current knowledge; the term first appeared in print in 1957. Soft science fiction points the same futures at psychology, sociology and politics, and treats the technology as substrate rather than subject.

Treat the pair as a promise about where your rigor budget goes. The hard reader audits the machinery and will catch the drive that outruns its own rules; the soft reader audits the society and will catch the institution that behaves as the plot requires. Critics quoted across the two articles (Gary Westfahl on the terms being useful approximations rather than a taxonomy, Ursula K. Le Guin on the disdain for the "soft" sciences) agree the boundary is a slope, and the practical answer stands: choose the scrutiny you invite before chapter one, then pass it. At the far end of the spectrum sits space opera, which trades auditability for mythic scale and says so honestly.

Worldbuilding with consequence discipline

Science fiction worldbuilds by extrapolation: change one thing, then follow it through money, law, manners, language and war. That is worldbuilding in the strict sense, and the genre's version has a discipline the catalog covers twice over: write the world's rules down, and give every power costs and limits before the plot leans on them. The invented drive, drug or network is canon from its first sentence; a later chapter that quietly upgrades it is the SF form of a broken magic system.

One habit separates the genre's best work from its wallpaper: consequence at every scale. If the teleporter exists, ask what happened to the shipping industry, the city gate, the hostage negotiation, the sentence "I need some space". You will not use all of it, but the parts you use are where the story lives.

Where SF meets web fiction

The genre's idea-first tradition feeds web fiction's biggest shelves directly, and the catalog covers the landing points:

• [System apocalypse](/learn/system-apocalypse-guide) bolts SF's collapse engine to game mechanics arriving involuntarily: the idea is an event, and its consequences are the plot.
• [Dungeon core](/learn/dungeon-core-guide) makes the system itself the protagonist: management, economy and ecology instead of a hero's journey.
• [LitRPG](/glossary/litrpg) puts the world's rules on the page as numbers, which is the hard-SF instinct of stated rules and audited consequences wearing game clothes.

If your strength is rule design and consequence discipline, those shelves reward it; the LitRPG guide covers the system design work they all share. Whichever shelf you choose, the contract is the same one Asimov stated: the change is the premise, the human reaction is the story, and the rigor you promised is the craft.