Copyleft vs. open source

Volumes have been written about open source and what it means, the various open-source licenses that are available, and how copyleft fits into the whole scheme of things. For software developers, business owners, and anyone else with an interest in exploring how software copyright works, an understanding of the basics of open source and copyleft can be a helpful when determining which type of license to use to distribute your software.

Overview of open source

For many people, "open source" means "free," but that is an overly simplistic description of a far more complex philosophy. The focus of an open-source license is a permissive, or open, stance on what users can do with the original source code.

In order for software to be open source, it must adhere to 10 criteria established by the nonprofit Open Source Initiative. These criteria deal with how source code can be accessed, modified, used, and distributed.

The most important concept to grasp is the difference between software that is commercial in nature and software that is proprietary. While open-source software can be commercial, it can never be proprietary. When software is proprietary, it uses closed-source code, which means that not only can users and developers not modify the code, the company distributing the proprietary software doesn't even release the code with the product.

On the other hand, all open-source software must, by virtue of it being distributed under an open-source license, include the source code, which can then be freely used, modified, or shared by anyone. However, certain terms and restrictions may apply, depending on the type of open-source license the software is distributed under.

Some well-known examples of open-source software include:

• Linux operating system
• MySQL database program
• LibreOffice office suite
• Android operating system
• WordPress blog platform
• Mozilla Firefox web browser

Overview of copyleft

Copyleft is a subset of open source. Contrary to what the term might imply, copyleft is not the opposite of copyright. In fact, copyleft is grounded in the concept of copyright, without which copyleft couldn't exist. Before someone can license software under a copyleft license, they must first own the copyright to that software, thus giving them the right to distribute it.

Both open source and copyleft allow for source code to be modified and distributed. However, the difference is that with copyleft, the modified product must be distributed with the same copyleft license attached to the original software. This allows for creation of derivative work based on the source code covered by the copyleft license while protecting the original creator's interests.

For example, Bob owns the copyright to original software, which he decides to distribute under a copyleft license. Gemma downloads Bob's software, modifies it, and then distributes her modified version. Gemma must distribute her modified version under the same copyleft license that Bob used. Anyone who then modifies Gemma's version must also distribute it using Bob's same copyleft license.

Both open source and copyleft are complex terms that deal with a user's right to access, use, modify, and distribute a work that is based on the source code of another piece of software. Understanding the basics of both concepts is crucial when modifying or distributing any form of software or computer code.