[pp.int.general] Patent system similar to GPL?

[Richard Stallman]

Copyleft applies to works that contain code derived from your work.
It requires those works' copyrights to be licensed under the same
copyleft license, so that they permanently carry that license, even a
century or two from now when your copyright has expired.

This requirement applies to the modified work as a whole.
Whoever makes the modified work has the copyright on that modified work,
and thus has the legal power to release it as copyleft requires.

If he wants to use pieces he got from others, he is required to follow
the copyleft license for the whole resulting program, including those
pieces.

Copyright covers copying (in a broad sense).  He can tell if he is
copying something, so he knows which code's copyrights are going to be
relevant to the combination he makes.  Copyright explicitly does not
cover ideas.  So if there is some code he can't get permission to use
in the copylefted combination, he does have the option of replacing
that code from scratch.  (This may be a lot of work.)

But you can't tell when you infringe a patent.  A patent is not
attached to a particular part of a particular product.  A patent is a
monopoly on an idea.

So if you try to make a "similar" arrangement to copyleft using patent
law, you won't get similar results.  A product that uses your patented
idea surely uses many other ideas.  The person who designs this
product may not have or get any relevant patents, but third parties
probably have some, and the designer often won't know they exist.

If you insist that ALL those patents be licensed out to the public,
the problem is that (1) he doesn't know what they are, and (2) when he
does know of some patents, he has no leverage to persuade their third
party holders to agree.

However, if you don't insist on this, the third party patent holders
will ruin the desired effect.

-- 
Dr Richard Stallman
President, Free Software Foundation
51 Franklin St
Boston MA 02110
USA
www.fsf.org, www.gnu.org