Permissive vs Copyleft Licenses: Key Differences Explained

Permissive vs Copyleft Licenses

The most important classification in open source licensing is the distinction between permissive and copyleft licenses. Understanding this distinction is essential for making informed licensing decisions.

Permissive Licenses

Permissive licenses allow users to do almost anything with the code, including incorporating it into proprietary software. The main requirement is typically attribution (keeping the copyright notice).

Examples: MIT, ISC, BSD-2-Clause, BSD-3-Clause, Apache-2.0

Key characteristics:

• Derivative works can be proprietary (closed source)
• Minimal conditions — usually just attribution
• Maximum freedom for downstream users
• Widely used in libraries and developer tools

Copyleft Licenses

Copyleft licenses require that derivative works be distributed under the same (or compatible) license terms. This ensures the code and all its derivatives remain free and open source.

Examples: GPL-2.0, GPL-3.0, AGPL-3.0, LGPL-3.0, MPL-2.0

Key characteristics:

• Derivative works must remain open source
• Source code must be made available
• Stronger protection for software freedom
• Can limit commercial adoption

Copyleft Strength Spectrum

Strength	License	Scope
Strongest	AGPL-3.0	Entire program + network use
Strong	GPL-3.0	Entire program
Weak (library)	LGPL-3.0	The library itself
Weak (file)	MPL-2.0	Modified files only

The Real-World Impact

Consider a company that wants to use your library in their proprietary product:

• MIT/Apache-2.0 — They can use it freely, just need to include your license
• LGPL-3.0 — They can link to your library but must share changes to the library itself
• GPL-3.0 — Their entire product must be open source if they distribute it
• AGPL-3.0 — Even running it as a service requires open-sourcing their code

Which Is "Better"?

Neither is inherently better. Permissive licenses maximize adoption and simplicity. Copyleft licenses maximize software freedom and community contributions. Your choice depends on your values and goals.