trochee

[note: if you're already a free software geek, this is undoubtedly review. But I figured if I'd written the explanation, then it's more useful if it's more shared.]

A friend -- who's really quite sharp on computer stuff, given no training -- asked two of us in my lab about classification algorithms and decision trees. The other guy in the lab pointed out IND and MatLab and cc'ed me; I pointed out another:

There is also c4.5, from Ross Quinlan, but he has decided to try to make money off the software so it's not Free as in Speech. (but it's still Free as in Beer, and you can download c4.5 from here).

But the friend said, quite rightly:

[trochee], I never did get this speech / beer distinction. Explain?

This is what I wrote:

ah, I see the problem. Look at the second paragraph of this web page. "free as in [free] speech, not free as in [free] beer" is an attempt to make the distinction between free/libre and free/gratis.
That is, "free" has two senses in English: "liberated" -- presumably from the constraints of encumbrances restricting the redistribution, like copyright -- and "without charge". Some software is free as in "free speech" without being free as in "free beer" -- the GPL, for example, allows redistributors to make it available for the cost of redistribution.
But the two meanings often apply to the same piece of software: I can download the Gnu C Compiler (gcc) for no money (free as in beer) and I can be sure that it won't be developed in a way that I can't contribute further (free as in speech).
Thus c4.5 is free-as-in-beer: no cost, but not free-as-in-speech because there are strong restrictions on the redistribution or modification of source. RQ doesn't want people patching his code, for example, because he is trying to make a buck off c5.0 and if people keep fixing c4.5 then it will become a community resource faster than he can keep up. Which is (if I may digress again) the reason that (1) c4.5 is not free-as-in-speech and (2) the general reason that a lot of big software companies *cough*micro*cough*soft*cough* are very afraid of letting bits of their code become free-as-in-speech.
does that help?

Well, does it?