Party A writes some software; perhaps intending to distribute it under the MIT or some other permissive license. THe software uses some GPL'd software. Party A conveys the software to party B, without conveying any of the GPL'd software; relying on B to obtain that software themselves. Does party A have to attach the GPL license to the conveyed software?

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    It's helpful to remember that copyright protects "copying", not "using". As an analogy, just imagine that you write a program that 'uses' Microsoft Windows APIs. When you distribute your program, you definitely don't need Microsoft's permission to do so, even though you 'used' their APIs. The confusion usually comes because when people say casually I used open source library libBLAH in my prorgram, what they actually mean, is that they copied/linked/compiled libBLAH, which creates a derivative work of libBLAH and does require permission.
    – Brandin
    Apr 2, 2020 at 4:29
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    The devil in these questions is in the details. You write "The software uses some GPL'd software", but what do you mean by that? It's dynamically linked to some GPL software? It uses that software through an API you worked out by reading the GPL code? It uses that software through a well-documented API? It calls that software through userspace and passes a complex database structure between them? It calls that software through userspace with two simple numerical arguments? We need to know a lot more to have any hope of being helpful. What are you using, and how?
    – MadHatter
    Apr 2, 2020 at 8:03
  • The GPL (and any enforceable licence), starts with copyright to lock you down, and then gives you permissions (freedoms). So if you do nothing that would breach the copy-right, then you don't need the licence. Apr 3, 2020 at 17:44


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