---
id: "prereq-fair-use-doctrine"
type: "prereq"
source_timestamps: ["¶5", "¶6"]
tags: ["legal-knowledge", "copyright"]
related: ["concept-fair-use-divergence"]
reason: "Understanding the four fair-use factors (especially 'transformative use' vs. 'market effect') is required to grasp why Judges Alsup and Chhabria reached opposite conclusions."
sources: ["tail2"]
sourceVaultSlug: "hbr-seg-tail2"
originDay: 2
articleStem: "hbr-tail-126-genai-copyright"
sourceUrl: "https://hbr.org/2025/07/can-gen-ai-and-copyright-coexist"
sourceTitle: "Can Gen AI and Copyright Coexist?"
---
# U.S. Fair Use Doctrine

**Prerequisite knowledge.** U.S. fair use (17 U.S.C. §107) is a four-factor, holistic defense to copyright infringement: (1) purpose and character of the use (including whether it is *transformative* and commercial), (2) nature of the copyrighted work, (3) amount/substantiality used, and (4) *effect on the market* for the original.

**Why it matters here:** the divergence in [[concept-fair-use-divergence]] turns on which factors the judges weight — [[entity-judge-william-alsup]] emphasizes transformativeness (factor 1), while [[entity-judge-vincent-chhabria]] emphasizes market effect (factor 4). A downstream expert should also know the doctrinal guardrails from *Authors Guild v. Google* (transformative search/snippet use) and *Andy Warhol Foundation v. Goldsmith* (2023) (new meaning insufficient if the use competes in the same market).