Copyfree: Unfetter your ideas.

Copyfree is not the same as copyleft.

The Free Software Foundation has this to say about copyleft:

Copyleft is a general method for making a program or other work free, and requiring all modified and extended versions of the program to be free as well.

The simplest way to make a program free software is to put it in the public domain, uncopyrighted. This allows people to share the program and their improvements, if they are so minded. But it also allows uncooperative people to convert the program into proprietary software. They can make changes, many or few, and distribute the result as a proprietary product. People who receive the program in that modified form do not have the freedom that the original author gave them; the middleman has stripped it away.

Understanding Copyleft

The key to understanding copyleft is in license heritability and the availability of copyrighted material:

  1. Copyleft licensing has very strong heritability characteristics. In essence, where document foo is covered by a copyleft license and document bar is covered by some other license, combining the two documents in a single work must, by law, result in a work available under the terms of the copyleft license.

  2. Copyleft licensing imposes restrictions on allowable forms of distribution. Specifically, where any part of a copyleft licensed work is distributed and the distributed portion is not in a "preferred" form for editing the work (i.e. "source" form), the source form must be distributed as well if the recipient so desires, and the recipient must be made aware of the availability of source form.

In addition, as a direct result of the above two necessities, a copyleft license also has the following characteristics:

  1. Copyleft licenses are dependent upon copyright law for their core characteristics to remain enforceable. One cannot legally enforce restrictions on redistribution, outside of a direct contractual agreement, without some form of copyright control in effect.

  2. Copyleft licenses are mutually incompatible. Any two copyleft licenses cannot in and of themselves be combined into a single, integrated work because of the conflicting heritability requirements of both.

Contrast With Copyfree

Meanwhile, a copyfree license must conform to the following requirements, as explained in the Copyfree Standard:

  1. Free Use
  2. Free Distribution
  3. Free Modification and Derivation
  4. Free Combination
  5. Universal Application

This contrasts sharply with the requirements of copyleft licensing, whose demands contradict the Free Distribution and Free Combination requirements of the Copyfree Standard.

Copyleft Licenses

A number of prominent free/open source licenses are copyleft licenses.