Open source software was born out of the idea that many people working together could produce better software—software that could be used by all who wanted it.
For a program to be open source, the source code must be freely available to its users. With ideal open source software, anyone can use and edit the code. There are no licensing fees or use restrictions, and anyone can pass it along, edited or not.
This method of development allows programmers around the world to come together and produce high-quality software. Each developer adds their knowledge, skill and experience to help the collective product. Most of the work on open source projects is done by volunteers that believe in or have an interest in the project. These programmers have produced some great work: Open source software is responsible for Ubuntu, Firefox, and WordPress (the platform used by this very website).
From a legal standpoint, open source software creates a lot of questions. Who owns the collective work? Does a developer own his or her edits? Can a developer distribute the software in binary form without source code? Can open source code be modified and sold? What happens when open source code is combined with proprietary code? Are there any warranties for the code? Who is responsible for deciding what edits make the final version?
The answers to these questions—if there are any—depend on the type of open source license that is used. There are many licenses, and each has its benefits and pitfalls.
Permissive licenses are the simplest form of open source licenses. The main, and sometimes only, requirement for using permissive licenses is to keep a copyright notice in the distribution of the corresponding open source software. Permissive licenses allow people to do pretty much whatever they want with the code: People can make edits to the code and sell it to customers without passing along the source code; and they can combine it with proprietary code. It easier for the developers as they can cut and paste code with little worry. Berkeley Software Distribution (BSD) is an example of a permissive license, and a sample of the license’s text can be found here.
Copyleft licenses are much more complicated. Copyleft licenses have what is sometimes called a viral or hereditary characteristic. Anyone who redistributes software must pass along the freedom to further copy or change it. The edits that a developer makes are not proprietary—meaning that if you use copyleft code, no matter how much work you put into it, the software cannot be distributed for profit. Some strong copyleft licenses can even force proprietary software to become open source if the code was designed to work with or to incorporate the open source code. This can be rather dangerous for developers. Copyleft scares away many commercial developers because they fear that the copyleft license will swallow up their proprietary code. This often leads to developers producing their own code or paying for a license rather than incorporating free open source code. The most prevalent copyleft license is the GNU General Public License GPL, and the text for the GPL version 2 can be found here.
But why was copyleft ever created? Permissive licenses seem better in many ways. Under permissive licenses, people can work together with little restriction. Programmers have more freedom to use already written code. Developers can design programs to work with proprietary software without the risk of losing the software to a copyleft license.
The answer to this question goes to the heart of open source software. When software is freely available, people can turn it into proprietary code. Under permissive licenses, people can take open source software, make some edits, and sell it, thus turn free software into a proprietary product. Copyleft combats this. Some of the freedoms of permissive licenses may be gone, but the software remains free. The goal of open source is better software that is free to the public—copyleft better fits that goal.*
*Ryan Rypka is the Technology Editor on the Michigan Technology Law Review. He can be reached at email@example.com.