Hello everyone, Following this discussion thread, it seems that great many developers are not sufficiently familiar with copyright and licensing of free and open source software (FOSS). A very good brief on this matter, which I can really recommend to everyone to read, is the 13 pages short publication "The Open Source Legal Landscape" by the Australian lawyer Brendan Scott. Follow this link to download it as PDF: http://opensourcelaw.biz/publications/papers/BScott_OSS_Legal_Landscape_0603... Please, notice that the paper discusses *Australian* law. The law of other jurisdictions may (or may not) be different. With Brendan's kind permission, I have below included the most interesting parts with respect to our discussion. 1.3 Copyright operates by prohibiting numerous categories of action in respect of a copyright work. [...] In the absence of a permission from the copyright holder, there is an absolute prohibition on exercising any of the rights comprised in copyright in respect of that work. 1.4 For example, if a person buys both a screwdriver and some software from someone, they may do what they like with the screwdriver, including modifying it, improving it, renting it to others etc. However, the scope of actions that they can undertake with the software is strictly limited (subject to some qualifications) to those things over which they have been granted permission from (ie licensed by) the holder of copyright in the software. [...] 2.3 [...] Open source licences effectively exempt the permitted activities from copyright infringement, subject to compliance with certain conditions (which are different depending upon the licence). A failure to comply with the conditions in the licence will mean that the activities are no longer exempted from infringement of copyright. If the activity in question results in an infringement of copyright, then the copyright owner will have an action against the person engaging in the activity. 4.1 Open source licensing is a customer driven market reaction to the high transaction costs and anti-competitive effects that the old model has produced. It effectively says that, through judicious use of copyright, customers can acquire software with rights analogous to ownership. In the example above, if the software is open source software, the person acquiring the software would have property-like rights over the use of the software in a manner analogous to the rights they have over the screwdriver. 7.1 One of the characteristics of open source licences is that they must “/permit”/ the source code of modifications to the software to be licensed under an open source licence. [...] Some open source licences go further, not only permitting, but /requiring/ that modifications of the software or other, related, software be licensed under an open source licence, typically under the terms of the same licence. [...] 7.2 The GNU General Public License (GPL) is the best known, and perhaps the most widely implemented of the strong licences. It requires that if modifications to GPLed software are published or distributed, they must be licensed under the terms of the GPL. It further requires that works which: (a) include as part of them a modification of software licensed under the GPL; and (b) which are distributed must also be licensed under the GPL and that access to the source code of the software must also be provided. [...] 9.1 One of the consequences of strong licensing is that care must be exercised when combining source code from two or more different projects which are licensed under different licences. [...] If the requirements of these licences are /per se/ inconsistent then there is no legal basis on which the output product can be licensed. 14.5 The GPL permits the making of changes to the software and does not require the distribution of changes made. However, if you do distribute those changes, and they are “derived from” the software, you must distribute those changes on the terms of the GPL. This makes the GPL a strong licence. [...] I have deliberately omitted the paper's definition of "strong licence" above. That is because Brendan, in private correspondence, has asked me to downplay the characterization because he is increasing coming to the conclusion that distinction between "weak" and "strong" licenses is not all that clear. Please, read the full publication which can be downloaded from the web site of Open Source Law <http://www.opensourcelaw.biz/>. Best regards, Thomas (IANAL)