Understanding Open Source License Definition: Types and Comparison

With the rapid expansion of the software development sector, the importance of open source licenses has surged dramatically, becoming an indispensable component in the software universe. The open-source movement, once the province of a few dedicated hobbyists, has evolved into a cornerstone of modern technology, revolutionizing the way we work together, innovate, and develop new tools and services. But to what extent do you understand the various types of open source licenses, and how they mold the process of software development?

Having honed my legal expertise at the University of Florida Levin College of Law, and now boasting a decade of experience as an attorney with an emphasis on open source technologies, I am well-positioned to guide you through this labyrinth of open source licensing. My extensive experience has afforded me a deep understanding of the intricate relationships between open source licensing, software development, and the broader legal landscape.

In this article, I intend to take you on an exploratory journey through the vast landscape of open source licensing. We will scrutinize its diverse forms, dissect their implications, and comprehend how they shape the entire software development ecosystem. Let’s initiate this journey by understanding the definition of an open source license.

Short Summary

  • Open source licenses are legal instruments that protect the rights of creators and users while providing access, modification, and dissemination of software’s source code.
  • Open Source works are governed by licenses with varying levels of protection. Copyleft licenses can be classified as strong or weak depending on derivative work definitions whereas permissive ones offer flexibility for use & distribution.
  • Choosing an appropriate license requires careful consideration to prevent any legal complications while leveraging its benefits such as collaboration & innovation in software development.

Defining Open Source Licenses

Open source licenses are legal instruments that facilitate access, modification, and dissemination of software’s source code. These licenses provide a legal framework that fosters collaboration and innovation in the open-source software ecosystem while protecting the rights of creators and users.

Open-source licenses generally grant users the right to:

  • Access, modify, and distribute a piece of software’s source code, subject to certain conditions
  • Give credit to the original author
  • Contribute any modifications back to the community

Understanding open source software licenses is vital for both authors and users, as it is imperative to comprehend the terms and conditions of the license, as well as the consequences of utilizing and modifying open source software.

To better understand the nuances of open source licensing, it’s essential to differentiate between open source software and proprietary software, as well as how open source licenses compare to public domain works. Let’s explore these distinctions in the following subsections.

Open Source Software vs. Proprietary Software

Open-source software is publicly accessible and modifiable, whereas proprietary software is owned and restricted from being freely employed, disseminated, or altered by others. This fundamental difference has significant implications for the way software is developed, distributed, and used.

In some cases, open-source software may be combined with proprietary software in separate files, depending on the specific license terms. On the other hand, source-available software, a marketing term for proprietary freeware, comes with source code provided for reference purposes but does not allow for the creation of derivative works.

As a result, the end-user license agreement for proprietary freeware typically precludes users from participating in the development process.

Open Source vs. Public Domain

Open-source denotes software or other works that possess an open-source license, which permits for free utilization, alteration, and circulation. In contrast, public domain encompasses works that are not confined by copyright and can be utilized, modified, and circulated without limitation.

The BSD license is an example of a permissive open-source license designed to enable free usage with no obligations imposed on users. Subsequent versions of the BSD license have further abridged the limitations, showcasing the evolution of open source licensing in response to changing needs and expectations.

Classifying Open Source Licenses: Copyleft and Permissive

Open-source licenses are generally divided into two major categories: copyleft and permissive. These licenses provide different levels of protection, flexibility and permission for the user. Copyleft licenses require users to share changes they make to the software. They must also make the source code of those changes available to the public. On the other hand, permissive licenses permit for greater versatility in utilization and distribution, including the formation of closed, proprietary derivative works.

By understanding these two main categories, we can better appreciate how open-source licenses shape the software landscape and influence the choices developers make in their projects.

Copyleft Licenses Explained

Copyleft open-source licenses require derivative works or modifications made to the software be released under the same licensing agreement. This ensures that the source code remains free and open for general use. This requirement encourages collaboration and sharing, as it ensures that any improvements or additions made to the software remain freely accessible to all.

However, copyleft licenses can be further classified into strong and weak copyleft licenses, with the former encompassing a wide definition of derivative works and the latter having a more limited interpretation. For example, GPL v2, GPL v3, and AGPL are examples of strong copyleft licenses, while the Mozilla Public License (MPL) maintained by the Mozilla Foundation is a weak copyleft license.

The LGPL, or Lesser General Public License, is another example of a copyleft license that falls somewhere between strong and weak copyleft licenses. It permits users to link the software with other proprietary software without necessitating them to disclose the source code of the proprietary software.

By understanding the differences between strong and weak copyleft licenses, developers can better choose the appropriate license for their projects based on their desired level of control and collaboration.

Permissive Licenses Unveiled

Permissive licenses, on the other hand, offer a high degree of flexibility in terms of use and distribution, including commercial use, and permit the creation of closed, proprietary derivative works. Businesses and individuals alike prefer open-source licenses due to the flexibility they offer with regards to using open-source software. Such freedom extends to manipulating these components to create proprietary software.

However, a permissive license may result in the generation of closed, proprietary derivative works, which could be seen as a drawback depending on the developers’ goals and intentions. Most permissive licenses typically include disclaimers of warranty and the obligation to credit authors, ensuring a balance between freedom and responsibility.

Popular Open Source Licenses: A Closer Look

While there are numerous open-source licenses available, some of the most widely utilized ones are:

  • The GNU General Public License (GNU GPL)
  • The Apache License
  • The MIT License
  • The BSD License

Each of these licenses has its own characteristics, advantages, and limitations, which can impact the way software is developed and distributed under the same license.

By examining these popular licenses in more detail, we can better understand their implications and how they shape the software development landscape.

Notable Permissive Licenses

Among the popular permissive licenses, the following stand out as widely used options.

  • The MIT License: a permissive open-source license that enables users to modify, distribute, and utilize the software for any purpose, provided that the original copyright and license notices are preserved.
  • The BSD License: a permissive open-source license that allows users to modify and distribute the software, as long as the original copyright and license notices are preserved.
  • The Apache License: a permissive open-source license that allows users to modify and distribute the software, as long as the original copyright and license notices are preserved.

The BSD License is another permissive open-source license that facilitates users to:

  • Modify, distribute, and utilize the software for any purpose
  • Preserve the original copyright and license notices
  • Not hold the original author accountable for any damages.

The Apache License is an open-source license that permits users to modify, distribute, and utilize the software for any purpose, provided that the original copyright and license notices are preserved. By understanding the nuances of these notable permissive licenses, developers can make informed decisions about which license best suits their project goals and requirements.

Renowned Copyleft Licenses

In terms of popular copyleft licenses, some of the most prominent examples include:

  • GNU General Public License (GNU GPL)
  • Mozilla Public License (MPL)
  • Eclipse Public License (EPL)
  • Lesser General Public License (LGPL)

The GNU GPL License is a widely utilized free software license that grants users the right to modify, distribute, and employ the software for any purpose.

The MPL is a hybrid open-source license that combines elements of both the GPL and the BSD license, making it a unique option for developers looking for a balance between the two. The EPL is a weak copyleft license that necessitates the disclosure of modified code if it is distributed as part of the program’s source code, yet permits the provision of only object code for distribution.

The LGPL, as mentioned earlier, is an open-source license that permits the utilization of open-source software in proprietary applications. By examining these renowned copyleft licenses, developers can better understand their options and determine which license best aligns with their project goals and desired level of control.

Navigating Open Source License Risks and Compliance

While open source licenses offer numerous advantages, they also come with potential risks and compliance issues. Permissive licenses allow the creation of closed, proprietary derivative works. This can lead to license compatibility issues when combining the software with other software under a different license. Adhering to licensing requirements is essential in order to prevent any potential legal complications.

Users can examine the license associated with the open-source software and ascertain compatibility in accordance with the stipulations outlined in the license. A notable example of a legal dispute involving open-source licenses is the lawsuit between Microsoft and OpenAI, where it was alleged that they had violated intellectual property rights by utilizing open-source code created by third parties and published on GitHub without permission.

Choosing the Right Open Source License for Your Project

Selecting the most appropriate open-source license for a project is crucial, as it can impact the manner in which the software is utilized, distributed, and modified. Developers should consider factors such as project goals, community norms, and potential risks when choosing an open-source license. Assessing the reliability, reputation, and support of the license is also important, taking into account the degree of control desired, the intended purpose of the project, and the community that will be utilizing or developing against the software.

By carefully considering these factors, developers can make an informed decision about which open-source license best aligns with their project’s needs and goals.

License Compatibility in Open Source Software

License compatibility refers to the ability of two or more open-source licenses to be used simultaneously, and merged together in a single software project. This ensures that projects comply with the open source license requirements. Permissive licenses are generally considered compatible, as they can encompass distinct components of a project. However, not all licenses are compatible, and it is important to carefully review the terms of each license to ensure that they can be combined without conflicts.

For example, the Apache License 2.0 is compatible with GPL v3 but not with GPL v2. By understanding license compatibility and its implications, developers can avoid potential legal issues and ensure that their projects comply with the requirements of all involved licenses.

The Impact of Open Source Licensing on Software Development

Open source licensing has a significant impact on software development, including:

  • Allowing for collaboration and knowledge sharing amongst developers
  • Expediting issue resolution and improving product quality
  • Influencing the selection of business models for companies in the software industry
  • Affecting the regulations for the use and distribution of the software

The advantages associated with open-source licenses include fostering collaboration, innovation, and the development of high-quality software. However, open-source licenses may present certain risks and compliance issues, such as the potential for license violations, the requirement to comply with the terms of the license, and the necessity to ensure that the software is distributed in accordance with the license.


In summary, open-source licenses form the cornerstone of today’s software development landscape. Gaining insight into the subtleties of both copyleft and permissive licenses, including associated risks, compliance matters, and compatibility issues, empowers developers to select the most appropriate license for their unique endeavors.

As an attorney with a decade’s worth of experience, who sharpened my legal acumen at the University of Florida Levin College of Law and has since focused on open source technologies, I can’t stress enough the importance of understanding the implications of your chosen license. As the software development world continues its relentless pace of innovation and evolution, open-source licenses remain instrumental in guiding the path of collaboration, creativity, and accessibility within the industry.

Therefore, when you embark on your next software project, I urge you not only to contemplate the immediate impact of your license choice but also to consider its broader implications on the software development ecosystem. Remember, your decision can shape not only the trajectory of your project but also influence the wider open-source community and industry norms.

Frequently Asked Questions

What is meant by open source license?

Open source licenses are legally binding agreements that determine how users can access and modify the code of open-source software in accordance with the Open Source Definition. They enable users to freely use, modify and share the software as permitted by the Open Source Initiative’s license review process.

The Open Source Initiative’s license review process ensures that the licenses meet the Open Source Definition and are legally enforceable. This helps to protect the rights of users and developers, and to ensure that open source software remains freely available.

What is the difference between open source and licensed?

Open-source software is publicly accessible and can be modified by anyone, whereas proprietary software is owned by the company that made it and only they have access to the source code.

Open-source software offers many advantages over proprietary software, such as cost savings, flexibility, and the ability to customize the software to meet specific needs. It also allows for collaboration between developers, which can lead to faster development and more innovative solutions. Additionally, open to the public.

What are the two principal categories of open-source licenses?

The two principal categories of open-source licenses are copyleft and permissive licenses.

Copyleft licenses require that any derivative works must also be open-source and distributed under the same license. Permissive licenses, on the other hand, allow derivative works to be made.

How can I ensure that my open-source project is in compliance with the license of the software I am using?

To ensure compliance with the license of the software you are using, examine the license associated with the open-source software and ascertain compatibility in accordance with its stipulations.

What factors should I consider when selecting an open-source license for my project?

When selecting an open-source license, consider factors such as project goals, community norms, potential risks, and the reliability, reputation, and support of the license to ensure a successful project.

These factors should be carefully weighed to ensure that the license chosen is the best fit for the project. It is important to consider the implications of the license, such as the ability to modify the code, the ability to redistribute the code, and the ability to use the code.

Legal Disclaimer

The information provided in this article is for general informational purposes only and should not be construed as legal or tax advice. The content presented is not intended to be a substitute for professional legal, tax, or financial advice, nor should it be relied upon as such. Readers are encouraged to consult with their own attorney, CPA, and tax advisors to obtain specific guidance and advice tailored to their individual circumstances. No responsibility is assumed for any inaccuracies or errors in the information contained herein, and John Montague and Montague Law expressly disclaim any liability for any actions taken or not taken based on the information provided in this article.

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