And today we have Creative Commons which provides a rich array of 
licences to do this and many other things http://creativecommons.org/

Ken Friedman wrote:
> Copyleft
> 
> --
> 
> The following article is published as:
> 
> Friedman, Ken. 2002. “Copyleft.” In The Encyclopedia of New Media. Steve
> Jones, editor. Thousand Oaks, California: Sage Publications, Inc.,
> 96-97.
> 
> This article is copyright © by Sage Publications, 2002.
> 
> --
> 
> Copyleft
> 
> Copyleft is a license granting general permission to copy and reproduce
> intellectual property. The term “copyleft” was created to reverse the
> idea of copyright. Understanding copyleft requires understanding the
> basic aspects of copyright. 
> 
> Copyright reserves exclusive control of copyrighted property to its
> creator. The creator decides what rights to grant others. Each grant of
> rights is established under a specific agreement. The creator of a
> copyrighted work may elect to transfer copyright ownership to another
> individual or to a business. In this case, the new copyright owner takes
> over all rights of copyright control, and decides how to manage those
> rights.
> 
> Copyleft is a general license agreement granted by a copyright owner
> permitting anyone to freely use copyrighted property under specific
> terms.
> 
> Common terms of a copyleft license state that a copylefted work is
> freely available to all potential users. Copylefted software allows
> users to run, modify, copy, and distribute software on the condition
> that the source code remains is open and publicly available. Copyleft
> usually states that copylefted software must passed on with a copyleft
> license requiring successive users to accept and transmit copyleft. The
> license further requires modifications or improvements to copylefted
> software to be transmitted under copyleft.
> 
> Copylefted content is transmitted in much the same way and under similar
> agreements.
> 
> Some argue that copyleft involves placing copyrightable material in the
> public domain. Others argue that copyleft is a specific license granted
> under copyright law, and they argue that the international statutes
> governing copyright law are the mechanisms that establish and protect
> copyleft. 
> 
> In one sense, copyleft is a return to the earliest ideas of intellectual
> property. Copyleft embodies three traditional principles governing
> intellectual property before the industrial revolution. 
> 
> Before these laws, intellectual property was a common good based on
> three principles. 
> 
> The first principle is that knowledge builds on prior knowledge.
> Innovation embodies prior art, and even revolutionary ideas build on the
> knowledge that successful revolutions overturn. 
> 
> The second principle is that no one can truly own knowledge. Knowledge
> grows with use as a common property that increases through circulation
> while shrinking with disuse. This view asserts that we can only own
> knowledge by sharing it while knowledge as private property is a
> contradiction in terms.
> 
> The third principle is tradition. The traditional approach to knowledge
> calls for preservation and transmission. Traditional knowledge grows
> incrementally, and new knowledge must incorporate earlier knowledge to
> be acceptable. Traditions of knowledge build on precedent, including
> law, theology, philosophy, and mathematics. Modern science and
> scholarship also build on precedent by incorporating earlier knowledge
> or refuting it. 
> 
> Many cultures respect the traditional view of knowledge. This gives rise
> to different views on intellectual property. Japanese and Chinese
> scholars, for example, often treat scholarly ideas as a shared heritage
> that demands respectful incorporation into their writing. While this was
> also the practice in the West before the Renaissance, Western scholars
> today view some traditional forms of incorporation as plagiarism.
> 
> While Western property law allowed for the growth of personal property
> rights for all forms of property, some cultures that accept personal
> property for physical goods follow traditional law for intellectual
> property.
> 
> The development of capitalism and banking in fifteenth century Venice
> led to the first patent law of 1474. In 1709, England enacted the first
> copyrigIn recent years, however, two ideas challenged the idea of private
> property rights in mental creation. 
> 
> Knowledge develops in a complex sequence of interactions in communities
> of practice and learning, and in larger societies and economies.
> Intellectual property is inevitably predicated on prior work.
> Individuals contribute to the whole, shaping variations and giving
> specific form to the statements that constitute intellectual property.
> The philosophical position of copyleft is that communities have rights
> in knowledge along with individuals. Moreover, copyleft asserts that
> copyright itself is often used against individuals by a legal system
> that favors powerful interests over individual creators.
> 
> One of the important predecessors of copyleft was Buckminster Fuller.
> Fuller copyrighted and patented his work both to document his creation
> and to preserve the work for humankind while protecting it against
> monopoly control by the legal system.
> 
> Soon, artists began to experiment with notions of general copyright and
> anti-copyright. In the early 1960s, Fluxus publisher and impresario
> George Maciunas promulgated a publishing and performance strategy
> similar to the concept of the general public license that would emerge
> later. Other Fluxus artists began to circulate event scores and
> program-like project notes with specific permissions for use and reprint
> on condition of transmitting the copyright conditions. In the early
> 1970s, British Fluxus artist David Mayor developed an anti-copyright
> philosophy, complete with an anti-copyright mark in the form of a tiny
> (x) in a circle.
> 
> Copyleft itself probably began in the work of MIT computer expert
> Richard Stallman. In 1983, Stallman started an open source programming
> project called GNU. He created the first general public license to
> govern the use of GNU, keeping it and its derivatives open and freely
> available.
> 
> Today, the concept of copyleft is central to many of the projects. Many
> actors in the information society, from software programmers and digital
> artists to content providers, composers, and designers, use it. 
> 
> Where copyright protects society’s interests in invention and creativity
> by providing individual incentives through copyright control, copyleft
> protects social interests in knowledge creation by vesting copyright
> control in a large, general community.
> 
> In one sense, it extends the benevolent hacker knowledge ethos that
> asserts, “Information wants to be free.” In another, it returns to the
> traditional concept of knowledge. This concept treats general ideas and
> their specific forms as a common heritage. Mental creations build on
> what has come before. They shape the platform of what comes next.
> Copyleft is a bridging mechanism developed to encourage the growth of
> social knowledge and common good.
> 
> -- Ken Friedman
> 
> Bibliography
> 
> Artlibre.org. “Free Art license. Copyleft Attitude.”
> http://antomoro.free.fr/c/lalgb.html
> Accessed 2001 June 2.
> 
> Jefferson, Thomas. 2001. “No Patents on Ideas. To Isaac McPherson
> Monticello, August 13, 1813.” The Letters of Thomas Jefferson:
> 1743-1826. The American Revolution - an .HTML project. Groningen, The
> Netherlands: University of Groningen, Department of Humanities
> Computing. URL:
> http://odur.let.rug.nl/%7Eusa/P/tj3/writings/brf/jefl220.htm/
> Accessed 2001 June 2.
> 
> Lillington, Karlin. 2001. “In Defense of Copyleft.” Wired Digital, 8:35
> a.m. Feb. 7, 2001 PST. URL:
> http://www.wired.com/news/politics/0,1283,41679,00.html
> Accessed 2001 June 2.
> 
> Stutz, Michael. “Copyleft and the Information Renaissance.”
> http://www.dsl.org/copyleft/
> Accessed 2001 June 2.
> 
> 
> Further Reading
> 
> Anderson, Judy. 1998. Plagiarism, Copyright Violation, and Other Thefts
> of Intellectual Property. An Annotated Bibliography with a Lengthy
> Introduction. Jefferson, North Carolina: McFarland and Company, Inc.,
> Publishers.
> 
> Buranen, Lisa, and Alice M. Roy. 1999. Perspectives on Plagiarism and
> Intellectual Property in a Postmodern World. Albany, New York: State
> UniversityCopyleft.net. “Geek Chic!” http://www.copyleft.net/index.phtml
> Accessed 2001 June 2.
> 
> Copyright and Copyleft. [Online resource collection.]
> http://www.edu-cyberpg.com/Internet/copyrightleft.html
> Accessed 2001 June 2.
> 
> Eisenstein, Elizabeth. 1983. The printing revolution in early modern
> Europe. Cambridge: Cambridge University Press.
> 
> Eisenstein, Elizabeth. 1979. The printing press as an agent of change.
> Communications and cultural transformation in early modern Europe.
> Cambridge: Cambridge University Press.
> 
> Febvre, Lucien, and Henri-Jean Martin. 1976. The coming of the book. The
> impact of printing 1450-1800. London: Verso.
> 
> Friedman, Ken with James Lewes. 1992. “Fluxus: Global Community, Human
> Dimensions.” Fluxus: A Conceptual Country. Estera Milman, editor.
> [Visible Language, vol. 26, nos. 1/2.] Providence: Rhode Island School
> of Design, pp. 154-179. [Special issue devoted to Fluxus, also
> exhibition catalogue]
> 
> Fuller, Buckminster. 1969. Utopia or oblivion: the prospects for
> humanity. New York: Bantam Books.
> 
> Fuller, R. Buckminster. 1981. Critical path. New York: St. Martin’s
> Press.
> 
> Goldstein, Paul. Copyright’s Highway: From Gutenberg to the Celestial
> Jukebox. New York: Hill and Wang, 1995.
> 
> Huddleston, G. Roger. 1910. “Scriptorium.” The Catholic Encyclopedia.
> Vol. XIII. Online Edition 1999. New York: Robert Appleton Company.
> Available from: URL http://www.newadvent.org/cathen/13635a.htm
> Accessed 2001 March 2.
> 
> Johnson, Emer D. 1970. History of Libraries in the Western World.
> Metuchen: Scarecrow Press, Inc.
> 
> LaFollette, Marcel C. 1992. Stealing into Print. Fraud, Plagiarism, and
> Misconduct in Scientific Publishing. Berkeley: University of California
> Press.
> 
> Rosenberg, Donald K. “Copyleft and the Religious Wars of the 21st
> Century.” [A talk for the Research Triangle Computer Law Roundtable, May
> 1997, revised for presentation at the Linux Expo in Durham, N.C., May
> 1998.] Stromian Technologies. http://www.stromian.com/copyleft.htm
> (2 June 2001).
> 
> Schwartz, Hillel. 1996. The culture of the Copy. New York: Zone Books.
> 
> Tate Gallery Archives. “Mayor, Fluxshoe, Beau Geste Press”
> http://www.tate.org.uk/collections/mayor.htm
> Accessed 2001 June 2.
>