17 U.S.C. 107 requires a case-specific fair-use analysis. Commentary, criticism, teaching, research, and other listed purposes can support a claim, but no label automatically makes copying lawful. The party asserting the defense generally bears the burden of supporting it. [1] [2]
Evaluate all four factors
- Purpose and character: what the use actually does, including commerciality and any distinct purpose.
- Nature of the work: factual or creative character and publication context.
- Amount and substantiality: quantity and qualitative importance relative to the purpose.
- Market effect: harm to relevant actual or potential markets.
The factors are weighed together; there is no universal safe number of words, seconds, notes, or percentage. Even a short excerpt can take the work’s core, while some justified uses can involve a complete work. [1] [3]
AI training is not one factual scenario
Questions can involve how copies were acquired, the particular training use, outputs, licensing markets, and the works involved. Do not infer that every AI-related use is fair or that the technology label alone defeats fair use. Current controlling decisions and the actual record matter.
Document the use before relying on it
Keep the source, amount copied, purpose, audience, distribution, alternatives, and market analysis. Permission or an appropriate license can be a different route from relying on an uncertain defense.
For example, quotation used to analyze a passage differs from supplying the passage as a substitute for buying the work.
Identify the market harm that copyright recognizes
The market inquiry is not simply whether a critical use makes the original less popular. A review can reduce demand because readers dislike the work, while a substitute copy can displace purchases in a different way. Campbell discusses why criticism and market substitution cannot be treated as identical harms. [2]
Analyze the particular use rather than a different use someone could imagine. Copying to comment on a passage, copying to supply an entertaining excerpt, and distributing a replacement file can have different purposes and market effects. A new format, a disclaimer, or attribution does not automatically resolve the four factors. Attribution can be ethically useful without providing copyright permission. Similarly, a nonprofit user should document the actual purpose and amount rather than assuming its tax status supplies a complete defense. [1] [3]
See audio conversion and copyright and copyright attorney-fee rules for separate copying and litigation questions.
Primary sources
- 17 U.S.C. 107
- Supreme Court: Campbell v. Acuff-Rose Music, 510 U.S. 569
- About the U.S. Copyright Office Fair Use Index
Sources checked: October 31, 2026.