Licensing Considerations for Combining MIT and LGPL-licensed Code

When developing software, particularly in the open-source community, it's critical to understand the licensing requirements of different components. This article will help clarify the distinctions between the MIT and LGPL licenses, especially in the context of combining them within a single project.

LGPL Overview

The Lesser General Public License (LGPL) is a widely used license for software libraries and components. It allows developers to use, modify, and distribute the code while ensuring that the original LGPL-licensed code remains free and open. The LGPL aims to balance the rights of software developers and end-users to modify and distribute code.

Linking and Licensing

The decision on how to combine MIT and LGPL-licensed code hinges significantly on the manner in which they are linked. Here’s a closer look:

Dynamic and Static Linking

Dynamic Linking: When the LGPL-licensed code is linked dynamically (e.g., through a shared library), the resulting application can be licensed under MIT. However, it's essential to ensure that the LGPL source code remains accessible.

Static Linking: In contrast, if the LGPL-licensed code is statically linked (i.e., when its code is merged directly into the application), the entire application must adhere to the LGPL requirements. This means that the entire software must remain under the LGPL license, as per the terms of the LGPL.

Combined Works

Combined Works: If the software is considered a combined work where the LGPL-licensed code constitutes a significant part of the application, the entire project cannot be relicensed under MIT. The LGPL components must still comply with the LGPL terms.

Providing Access to Source

Regardless of whether the code is linked statically or dynamically, if the software is distributed, the developer must ensure that the original LGPL source code is accessible and the modifications made to it are provided. This is a core requirement of the LGPL.

Using the Two Licenses Together

It is entirely possible to use both MIT and LGPL-licensed code in a combined work. The software can retain its licensing based on how the components are integrated:

Merging Code

If the LGPL-licensed code is merged into the application (static linking), the application cannot be relicensed under MIT. The entire combined work must comply with the LGPL.

However, if the LGPL-licensed code is used in a separate, dynamically linked library, the application can be licensed under any license you desire, including MIT.

Commercial Distribution

Both the MIT and LGPL licenses permit commercial distribution, provided the terms of the LGPL are met in the context of dynamic linking. As an experienced lead in a Free Software project (GNUstep), I can confidently say that you can distribute your software commercially while still adhering to the necessary licensing requirements.

Conclusion

The line between MIT and LGPL licenses can be fine, but understanding the nuances is crucial. Whether you can relicensed the entire software under MIT depends on how the LGPL-licensed code is integrated. Always ensure that you adhere to the terms of the LGPL, particularly in the context of dynamic linking, to avoid legal issues.

For detailed advice, it's wise to consult a legal expert. However, the insights provided here should help guide your development process and ensure compliance with licensing requirements.