Fair use is a defence, not a permission slip

Nobody grants you fair use

Fair use is section 107 of the US Copyright Act, and it operates as an affirmative defence. That word does a lot of work: the copying is admitted, and the argument is about whether it should be excused — so the question only gets answered once somebody has sued you and a judge has heard both sides. There is no register of fair uses, no clearance certificate, and no way to establish in advance that yours qualifies.

The Copyright Office puts it as directly as a government agency can: courts decide fair use case by case, and no formula guarantees that a set percentage or amount of a work — a number of words, lines, pages or copies — may be used without permission. Every rule of thumb you have heard is somebody's summary of a case with its own facts.

The four factors, and the two that usually decide it

Section 107 lists four factors, and courts must weigh all of them together rather than tallying scores.

1. The purpose and character of the use — whether it is commercial, and whether it does something meaningfully different from the original.
2. The nature of the copyrighted work — creative and unpublished works get more protection than factual, published ones.
3. The amount and substantiality used — measured against the whole work, and against whether you took the heart of it.
4. The effect on the market — for the original and its derivatives, including the market for licensing the very use you made.

In practice the first and fourth carry most of the weight, and they interact: a use with a genuinely different purpose rarely substitutes for the original, and a use that substitutes is rarely found transformative. The middle two seldom decide a case alone.

Four things people believe are the test, and are not

What the Supreme Court did to "transformative"

For twenty years the winning move in a fair use argument was to say the new work was transformative — that it added new meaning or message. In May 2023 the Supreme Court decided Andy Warhol Foundation v Goldsmith 7–2 and narrowed that considerably.

The Foundation licensed a Warhol silkscreen of Prince, made from Lynn Goldsmith's photograph, to a magazine to illustrate an article about Prince. Goldsmith licensed photographs to magazines to illustrate articles about musicians. Where the original and the challenged use share substantially the same purpose and the use is commercial, the Court held, the first factor favours the copyright owner — and new expression alone is not enough. The transformation has to go beyond what would merely make the work a derivative.

Appellate courts have applied that reading consistently since. In 2024 the Fourth Circuit found cropping a photograph to illustrate an article was not transformative, the Second Circuit said the same of format-shifting print books into lending copies, and the Eighth Circuit of putting a well-known meme in a fundraising email. Restyling, reformatting and recontextualising are not, by themselves, a new purpose.

Where fair use genuinely does work

None of this makes the defence narrow. It makes it purposive. The uses that succeed share one feature: the copying was necessary to do something the original was not doing.

• Criticism and commentary. Quote what you are discussing, at the length the discussion needs. A review that reproduces the work in full and comments briefly has the ratio backwards.
• Parody. Campbell v Acuff-Rose (1994) held a commercial rap parody could be fair use. The distinction that matters is that parody comments on the original; satire borrows a work to comment on something else, and has to justify why it needed that work at all.
• News reporting. Showing the thing being reported on, not using a news peg to republish someone's photograph as illustration.
• Teaching and scholarship. Classroom and research use, in the amount the teaching requires. "Educational" as a label on a commercial product is not the same thing.
• Search and indexing. Thumbnails in image results were held highly transformative in Perfect 10 v Amazon (2007): a search engine turns an image into a pointer to information.

AI training: two questions answered, the important one open

The AI cases have split a question people used to treat as one. How the copies were obtained, whether training on them is transformative, and what the model then outputs are three separate issues, and courts have gone different ways on each.

The open question is market harm. In Kadrey the judge accepted the fair use argument on the record in front of him while noting that a theory of market dilution — models flooding the market with works that compete with the originals — could well succeed on better evidence. That is the argument to watch, and it is being run in the consolidated OpenAI litigation now in discovery. If you build on AI output, your exposure is less about training data than about whether your outputs reproduce recognisable expression. Who owns AI-generated content covers the ownership half.

The UK and the EU do not have fair use

This is the commonest mistake made by anyone applying American advice outside America. UK law has fair dealing, which is not a general balancing test: the use must first fall within a named permitted purpose, and only then is it assessed for fairness — whether a fair-minded and honest person would have dealt with the work that way, looking at market substitution and how much was taken. EU law runs on a closed list of exceptions in the InfoSoc Directive, with no open-ended residual defence.

For AI specifically, the EU took the opposite route from litigation: Article 4 of the 2019 Copyright Directive permits text and data mining unless the rights holder has reserved its rights in a machine-readable way. That is an opt-out regime, not a fairness test, and it means the same training run can be lawful in one jurisdiction and contested in another.

A defence is not a licence, and the difference is money

The point that gets lost in every fair use discussion: even a winning defence is expensive. Warhol reached the Supreme Court. Being right is the outcome after years of litigation, not instead of it. A licence is certainty bought in advance for a known price — a content licence for stills and copy, a music licence for anything with a soundtrack. And where a licensing market plainly exists for exactly what you want to do, its existence cuts against you on the fourth factor anyway.

And if you are on the other side — someone has taken your work and is calling it fair use — the question is not whether they changed it, but what their use is for. If it does the same job as yours for the same audience, the label does not matter much. Someone copied my work sets out what works from there, and a copyright infringement notice is usually the first step.