Fair use of copyright, from the US Court of Appeals for the Second Circuit’s ruling in Authors Guild vs Google Books:
The ultimate goal of copyright is to expand public knowledge and understanding, which copyright seeks to achieve by giving potential creators exclusive control over copying of their works, thus giving them a financial incentive to create informative, intellectually enriching works for public consumption. This objective is clearly reflected in the Constitution’s empowerment of Congress “To promote the Progress of Science… by securing for limited Times to Authors… the exclusive Right to their respective Writings.” Thus, while authors are undoubtedly important intended beneficiaries of copyright, the ultimate, primary intended beneficiary is the public, whose access to knowledge copyright seeks to advance by providing rewards for authorship.”