Copyleft vs permissive licenses
The difference in one sentence: a permissive license asks you to keep notices; a copyleft license requires some or all of the derived work to stay under the same license when you distribute it. Which parts — single files, modules, a library, or the whole work — is the scope, and scope is what separates the copyleft families.
All 16 licenses by category
| License | Category | Same-license requirement covers | SaaS triggers disclosure |
|---|---|---|---|
| Unlicense | Public domain | — | No |
| CC0-1.0 | Public domain | — | No |
| MIT | Permissive | — | No |
| BSD-2-Clause | Permissive | — | No |
| BSD-3-Clause | Permissive | — | No |
| ISC | Permissive | — | No |
| Apache-2.0 | Permissive | — | No |
| BSL-1.0 | Permissive | — | No |
| MPL-2.0 | Weak copyleft | modified files | No |
| EPL-2.0 | Weak copyleft | modified modules | No |
| LGPL-2.1 | Weak copyleft | the library itself | No |
| LGPL-3.0 | Weak copyleft | the library itself | No |
| GPL-2.0-only | Strong copyleft | the whole combined work | No |
| GPL-2.0-or-later | Strong copyleft | the whole combined work | No |
| GPL-3.0-only | Strong copyleft | the whole combined work | No |
| AGPL-3.0 | Network copyleft | the whole work, incl. network use | Yes |
What permissive means in practice
Permissive licenses combine freely with each other. From the dataset's rule for permissive-with-permissive combinations: "Combine freely; retain all notices. Result can be relicensed (kept proprietary) downstream." Commercial, closed-source redistribution is allowed; the obligations are notice-level — and per the binary-distribution rule, "Permissive: include notices (Apache also needs NOTICE + change statements). Weak copyleft: disclose only the modified library/files and, for LGPL static linking, provide a relink path. Strong copyleft (GPL): NOT possible to keep proprietary if GPL code is in the derivative work. AGPL: same as GPL plus network rules."
What copyleft means — three scopes
- Weak copyleft limits the same-license requirement to the copyleft-licensed parts: modified files (MPL-2.0 — "File-level copyleft. Modified MPL files must stay MPL and be disclosed; your own new files can be any license. GPL-compatible via secondary-license mechanism (unless a file is marked 'Incompatible With Secondary Licenses')."), modified modules (EPL-2.0), or the library itself (LGPL). Your own code can stay proprietary.
- Strong copyleft (the GPL family) extends the requirement to the whole combined work when distributed — a closed-source binary is not possible.
- Network copyleft (AGPL-3.0) goes one step further: "GPLv3 PLUS a network clause: making the software available over a network (SaaS) counts as distribution, so you must offer source to remote users. The clause that catches startups who assumed SaaS never 'distributes'."
Note the SaaS column above: per the dataset's hosting rule, "Permissive and weak copyleft: no source disclosure. GPL/LGPL: no disclosure either (hosting is not distribution). AGPL: YES, you must offer source to users interacting over the network. This is the decision that most often surprises people."
Which should you use?
That depends on what you're combining and how you ship. Run your actual license set through the checker for a verdict and obligations, or start from a specific license's page. For choosing a license for a brand-new project, GitHub's choosealicense.com is the standard reference.
FAQ
- What is the difference between a permissive and copyleft license?
- A permissive license only requires you to keep notices; the combined work can be relicensed, including kept proprietary. A copyleft license requires some or all of the derived work to stay under the same license when distributed — the scope (files, modules, library, or whole work) is what varies.
- What is an example of a permissive license?
- MIT, BSD-2-Clause, BSD-3-Clause, ISC, Apache-2.0, and BSL-1.0. All six permit commercial use and closed-source redistribution with notice obligations only; Apache-2.0 adds an express patent grant and a NOTICE file requirement.
- Is copyleft bad for commercial use?
- No — commercial use is permitted by every copyleft license here. The constraint is distribution: weak copyleft only requires disclosing the copyleft-licensed parts, while strong copyleft requires the whole distributed work to be open-sourced. Hosting as SaaS triggers disclosure only under AGPL.