Copyleft

Copyleft, distinguished from copyright, is the practice of offering people the right to freely distribute copies and modified versions of a work with the stipulation that the same rights be preserved in derivative works created later. Copyleft software licenses are considered protective or reciprocal, as contrasted with permissive free-software licenses. Copyleft is a form of licensing, and can be used to maintain copyright conditions for works ranging from computer software, to documents, to art, to scientific discoveries and instruments in medicine. In general, copyright law is used by an author to prohibit recipients from reproducing, adapting, or distributing copies of their work. In contrast, under copyleft, an author must give every person who receives a copy of the work permission to reproduce, adapt, or distribute it, with the accompanying requirement that any resulting copies or adaptations are also bound by the same licensing terms. Copyleft licenses for software require that information necessary for reproducing and modifying the work must be made available to recipients of the binaries. The source code files will usually contain a copy of the license terms and acknowledge the authors. Copyleft type licenses are a novel use of existing copyright law to ensure a work remains freely available. The GNU General Public License (GPL), originally written by Richard Stallman, was the first software copyleft license to see extensive use, and continues to dominate in that area. Creative Commons, a non-profit organization founded by Lawrence Lessig, provides a similar license-provision condition called share-alike. Copyleft is a copyright licensing scheme in which an author surrenders some, but not all, rights under copyright law. Instead of allowing a work to fall completely into the public domain (where no ownership of copyright is claimed), copyleft allows an author to impose some restrictions on those who want to engage in activities that would more usually be reserved by the copyright holder. Under copyleft, derived works may be produced provided they are released under the compatible copyleft scheme. The underlying principle is that one benefits freely from the work of others, but any modifications one makes public must be released under similar terms. For this reason some copyleft licenses are also known as reciprocal licenses, they have also been described as 'viral' due to their self-perpetuating terms.Under fair use, however, the copyleft license may be superseded, just like regular copyrights. Therefore, any person utilizing a copyleft-licensed source for their own work is free to choose any other license provided they meet the fair use standard. According to Free Software Foundation compliance engineer David Turner, the term viral license creates a misunderstanding and a fear of using copylefted free software. David McGowan has written that there is no reason to believe the GPL could force proprietary software to become free software, but could 'try to enjoin the firm from distributing commercially a program that combined with the GPL'd code to form a derivative work, and to recover damages for infringement.' If the firm 'actually copied code from a GPL'd program, such a suit would be a perfectly ordinary assertion of copyright, which most private firms would defend if the shoe were on the other foot.'Richard Stallman has described this view with an analogy, saying, 'The GPL's domain does not spread by proximity or contact, only by deliberate inclusion of GPL-covered code in your program. It spreads like a spider plant, not like a virus.' While copyright law gives software authors control over copying, distribution and modification of their works, the goal of copyleft is to give all users of the software the freedom to carry out these activities. In this way, copyleft licenses are distinct from other types of free-software licenses, which do not guarantee that all subsequent recipients of the program receive these rights, or the source code needed to make them effective. In particular, permissive free-software licenses such as BSD allow re-distributors to remove some or all these rights, and do not require the distribution of source code.