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For example, if a person creates an application that they open-source under a license that says you can use this code but you cannot sell it, has that person just bound himself to not selling it now as well?

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up vote 5 down vote accepted

A license is the owner assigning rights and responsibilities over their intellectual property to a third party. Assigning one set of rights in one license does not preclude them from assigning a different set of rights and responsibilities to another third party.

This is how software products come to be dual-licensed or multi-licensed. Each license grants certain rights but imposes its own restrictions. Thus a software house may opt to release a software product under GPL for free, requiring derivations to be provided with source code, and under a closed source license, for a fee, where derivatives can be supplied without source code.

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Except that any community contributions to your GPL release are GPL - unless you can get the authors to assign ownership to you. – Martin Beckett Oct 3 '12 at 15:07
@MartinBeckett - Thanks I alluded to that in my linked answer, but I've updated it to make that more explicit. – Mark Booth Oct 3 '12 at 15:25
@MartinBeckett So you are saying that if I release my content under a certain license, if PersonB adds new content, the new content is bound by that license and not my property, correct? Is PersonB assigning rights, as Mark says in his answer, or is their addition bound to the license that I put on the overall code? – David Peterman Oct 3 '12 at 17:16
Yes if personB adds new functionality to the GPL code that new bit is owned by personB and is GPL. You can't take the new bits and add them to your closed source distribution without personB's permission. Remember GPL is all about distribution. Normally dual licensed apps will 'ask' that changes are assigned back to them, or won't accept any downstream changes at all – Martin Beckett Oct 3 '12 at 17:18
Hence why some consider the GPL a "virus" that "contaminates" everything downstream. :-) – Brian Knoblauch Oct 3 '12 at 20:28

You retain copyright and as long as you don't sign THAT away you can license your code under different licenses. Watch out though, it may turn out hard to remove a license once you put a license on a work.

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