I have to jump in here. I am a pattern designer and belong
to a pattern designer's collective. Copyright issues are discussed
regularly. The statement "My quilt instructor said that if a pattern is modified 40%, you can call it your own and sell it as your own and the items made" is completely wrong. When someone designs a pattern, provides the graphics and writes
the instructions, that pattern is their copyright. It is a complete misnomer that you can legally change a certain percentage of
the design and then call it your own. Also, the designer does have the right to say what can be done with that pattern and
limit whether or not items made from it can be sold, and if so, how many can be sold. I sure would like to know where the person got her facts that made the statement 'the designer doesn't have the right to tell you what you can or can't do, no
matter what they try to say'.
The suggestion that you look at Sylvia Landman's site is a great one. She is an authority on copyright laws and it clears up a lot.
Until you become a designer and try to make a living at it,
it is hard to understand the 'why' to some of these things, but
I can say that I have a completely different perspective on it
now that I am on this side of the coin and not just merely
someone who uses others patterns for my projects.