Why is LaTeX free?

Some words on the topic of free and paid software, from the mouths of the original creators:

Donald Knuth, the creator of TeX, from this interview (by Advogato aka Raph Levien) (republished in TUGboat):

Advogato: The first questions that I have are about free software. TeX was one of the first big projects that was released as free software and had a major impact. These days, of course, it's a big deal. But I think when TeX came out it was just something you did, right?

Prof. Knuth: I saw that the whole business of typesetting was being held back by proprietary interests, and I didn't need any claim to fame. I had already been successful with my books and so I didn't have to stake it all on anything. So it didn't matter to me whether or not whether I got anything financial out of it.

[Advogato:] I see.

[Knuth:] There were people who saw that there was a need for such software, but each one thought that they were going to lock everyone into their system. And pretty much there would be no progress. They wouldn't explain to people what they were doing. They would have people using their thing; they couldn't switch to another, and they couldn't get another person to do the typesetting for them. The fonts would be only available for one, and so on.

But I was thinking about FORTRAN actually, the situation in programming in the '50s, when IBM didn't make FORTRAN an IBM-only thing. So it became a lingua franca. It was implemented on all different machines. And I figured this was such a new subject that whatever I came up with probably wouldn't be the best possible solution. It would be more like FORTRAN, which was the first fairly good solution [chuckle]. But it would be better if it was available to everybody than if there were all kinds of things that people were keeping only on one machine.

So that was part of the thinking. But partly that if I hadn't already been successful with my books, and this was my big thing, I probably would not have said, "well, let's give it away." But since I was doing it really for the love it and I didn't have a stake in it where I needed it, I was much more concerned with the idea that it should be usable by everybody. It's partly also that I come out of traditional mathematics where we prove things, but we don't charge people for using what we prove.

So this idea of getting paid for something over and over again, well, in books that seems to happen. You write a book and then the more copies you sell the more you get, even though you only have to write the book once. And software was a little bit like that.

Leslie Lamport, creator of LaTeX, from this interview (republished in TUGboat):

GMZ: Was this always meant to be “free software”? Did you ever try to “get rich” with it? Do you regret that you didn’t?

LL: At the time, it never really occurred to me that people would pay money for software. I certainly didn’t think that people would pay money for a book about software. Fortunately, Peter Gordon at Addison-Wesley convinced me to turn the LaTeX manual into a book. In retrospect, I think I made more money by giving the software away and selling the book than I would have by trying to sell the software. I don’t think TeX and LaTeX would have become popular had they not been free. Indeed, I think most users would have been happier with Scribe. Had Scribe been free and had it continued to be supported, I suspect it would have won out over TeX. On the other hand, I think it would have been supplanted more quickly by Word than TeX has been.

One of the more coherent and influential documents advocating free software was Richard Stallman's GNU Manifesto written in 1985, revised 1987.

TeX and LaTeX come from around the same time (TeX in its present form from 1982, LaTeX from around 85 and latex2e from 1993). LaTeX isn't GPL and we probably don't make the same black and white moral/amoral classifications as Richard Stallman does, but anyway the Manifesto is a good read and a good introduction to why one might write software and give people freedom to modify it as they wish.

TeX and Metafont are academic works indirectly paid by Knuth's employer as part of his normal work, and Knuth needed these tools to produce his academic books and articles.. (His standards are just much higher than for most of the rest of us).

The academic tradition is that you share your stuff, to help your peers achieve even more. Knuth explicitly put TeX in the public domain to make this as easy as possible. The academic community has adopted this (typically in the LaTeX dialect) because nothing is better for writing advanced mathematics and as they know what you can achieve when you work together the ecosystem has continued the "stuff is available for free"-model because most people has a job already and they need this to do their job, so sharing freely is the model that works the best.

Note that commercial distributions of TeX have existed but with the proliferation of high quality Linux distributions with the necessary packages this is getting quite rare.

In other words, it started free and it works the best for the intended audience, so there is not much to commercialize.