Infringement is a question of fact rather than of intent. It is not a valid defense that the infringer is ignorant; nor, on the other hand, can any one be held for intention to infringe, where the act of infringement has not been accomplished. The new American code, nevertheless, recognizes knowledge and intent in certain cases of punishment or damages by the use of the words "willfully" and "knowingly." The letter of the law is in general that the infringer must be held responsible and must make good any damages suffered by the copyright proprietor, but proof that he had no guilty knowledge or intent may effect mitigation of punitive damages. The trend of court decisions and of judicial opinion does not seem to be evident and consistent in this development; but it may perhaps be said that while copyright law is more closely applied from the letter of the statutes, in the legal aspect, the principles of equity have been given freer play where the statute is not specific and definite. In 1899, in Green _v. Irish Independent_, the English Court of Appeal held that the proprietors of a newspaper who had printed an advertisement containing an illustration which the advertiser had license to use only for specified purposes, were liable for penalties, though they did not know that the illustration was copyrighted; and in 1902, in American Press Assoc. _v._ Daily Story Pub. Co., the U. S. Circuit Court of Appeals held the defendants liable, though they had innocently copied from a newspaper reprint which had inadvertently omitted the copyright notice. But in 1898 Justice Mathew, in Bolton _v_. London Exhibitions, declined to hold the defendants punishable, because they did not know that the lithographer from whom they had ordered a poster had infringed the copyright of a photograph. {Sidenote: "Fair use"} "Fair use" means quotation from or other use of an author's work within the evident meaning or judicial construction of the copyright statute, and is the usual answer of the defendant to a complaint that he has taken without authority some portion of the author's work or utilized in some way the result of the author's labors. The borderland between infringement and "fair use" is peculiarly and necessarily one of uncertainty, not so much because of ambiguity in the statute as of difficulty in determining the extent of use within which it is said _non curat lex_. No statute can be so clear or so complete as to obviate questions of this kind. In general there must be copying of a material or substantial part. What is a material or substantial part, constituting infringement, is a difficult question of fact. {Sidenote: Principle of infringement}