I'm trying to understand exactly when a work becomes a "derivative work," and how it affects licensing of my project. In my situation, we have a scientific code that we have written which is licensed under the MIT license. It uses the GNU Scientific Library (GSL) which is licensed under the GPLv3 (specifically not the LGPL). It is obvious to me that, once compiled and statically linked, the resulting binaries (and subsequently their source) must be distributed under the more restrictive GPLv3. However, we never distribute any binaries or any source licensed under the GPL. Therefore my question is:

Can I license and distribute source code under the MIT license which requires a GPL'd library to compile if I do not include anything derived from the GPL'd library? That is, does the dependency on a GPL'd library only "kick in" once compiled/linked into a binary? Or does the dependency itself mean that all source files which need to be linked with the GPL'd library need to be under the GPL as well?

I found the following questions before but they don't seem to quite answer my question:

  • Your 5th link is not actually related to this question - all the licenses in that question are permissive, and the attribution requirements only kick in if the library is distributed.
    – Max Xiong
    Sep 18, 2020 at 2:08

1 Answer 1


The FSF (owners of the GPL licenses) take the stand that by writing programs to the API of the libary creates a derivative work, that thus must be distributed under GPL. As far as I know (IANAL, even less one versed in copyright law and open source licensing), there are no legal precedents on the point.

Case in point is the (GPLed) readline libary. For quite some time, linking to it from non-GPLed programs was forbidden, until the drop-in replacement (BSD licenced) editline showed up.

  • I guess this is what people mean about the GPL being “viral” — since someone somewhere might download my code and link it to something GPL-licensed, I am required to license my own sources under the GPL rather than something more permissive.
    – kc9jud
    Sep 19, 2020 at 3:20
  • @kc9jud, that is by GPL's design.
    – vonbrand
    Oct 8, 2020 at 7:43
  • 1
    when did the situation change with readline? Now it just requires a GPL-compatible license, rather than specifically the GPL.
    – kc9jud
    Oct 9, 2020 at 2:09

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