Analogies

Sometimes analogies help to explain this to people new to the area.

Minefield

Richard Stallman has frequently mentioned this analogy in parts of his speeches:

• http://www.gnu.org/philosophy/stallman-mec-india.html
• http://www.gnu.org/philosophy/fighting-software-patents.html
• http://www.ifso.ie/documents/rms-2004-05-24.html

This analogy omits one aspect: when you step on a mine, you know it, but when you violate a patent, the patent holder might threaten you immediately, or might decide to let you continue to build you project on that idea and then threaten you.

Literature

Again citing Richard Stallman:

• http://www.gnu.org/philosophy/software-literary-patents.html

Music

Again citing Richard Stallman:

• http://www.ariel.com.au/a/rms-unsw.html
• http://www.abc.net.au/rn/science/buzz/stories/s1226098.htm
• http://news.zdnet.com/2100-3513_22-121749.html (2nd last section, "If symphonies were patented")