From an RMS interview:
http://some.net/transcripts/rms-19980613-gnu.log
<lilo> there's been a lot of recent discussion about the whole business with Qt
and KDE....I had
wanted to ask you, if you could, to talk about that whole business
<rms> just because it encouraged someone to use GNU/Linux.
<rms> Qt is a library which appears to be technically useful, but is not free
software.
<rms> Like all the other non-free programs out there, it's outside
<rms> of the free software community.
<rms> KDE is a free program which was developed so that it needs Qt in
<rms> order to run.
<rms> This has a paradoxical result: although KDE is free software,
<rms> it is useless as an addition to a free operating system,
<rms> because there is no way to run it on a free operating system.
<rms> In order to run KDE, you need to add Qt, which means that the operating system
is no longer
entirely free.
<rms> The KDE developers thought that they would "get the job done
faster"
<rms> if they used Qt--but the real result is that the wrong job got done.
<rms> It's like saying, "we can build this segment of track faster if we
don't
<lilo> okay, for some of our participants who are maybe not clear on the problem
with the Qt
license....I don't want to take a lot of questions on this, but could you tell us
what, in your
opinion, "breaks" the Qt license as free software?
<rms> make it connect with the other segment". Maybe so, but if it doesn't
connect,
<rms> you don't have a railroad that works.
<rms> I would have to look at the Qt license again; it has been several months
<rms> since I looked, and I don't remember.<lilo> okay, let's see....
<rms> I think it was either that it is limited to noncommercial distrbution only
<rms> or that distribution of modified versions is not allowed, or both.
* lilo nods
<rms> Either kind of restriction makes a program non-free; I just don't remember
for certain which
of these restrictions Qt has.
<rms> By the way, the Qt license says it gives permission to link Qt
<rms> with GPL-covered programs; however, if you actually do that, you would
<rms> violate the GPL.
<rms> If the authors of a GPL-covered program want to give permission for linking
it
<rms> with Qt, they can do so.
<lilo> so regardless of the flaws you see in it, it just simply doesn't work
connecting it to the
GPL<rms> It's clear that the authors of KDE mean to permit this, for example,
<rms> so it is permitted *for KDE*. But if you wanted to link Emacs with Qt
<rms> you would have to ask permission from the FSF, and I can tell you
<rms> that the answer would be no. The purpose of releasing Emacs under the GPL
<rms> is so that it can't be mixed with non-free software. Extended versions
<rms> of Emacs must be free software.