There is a schism in the Open Source movement between the Open Source People and the Free Software People. Think of the Catholics versus the Protestants, they reach similar conclusions from different premises.

Free Software

• Represented by the Free Software Foundation, the GNU people, and Richard Stallman
• Based on political beliefs
• Software should be free as in speech (as in the United States)
• Code is like a book, it is useless if no one reads it
• Free, as in price, does not matter, you can charge as much as you like for your work.

Open Source

• Represented by the Open Source Initiative, the poster boy is Erik Raymond
• Open Source produces higher quality software in a shorter period of time
• Free as in beer
• Protects users and businesses from bugs and security flaws
• Less duplicated work
• Monolithic design versus small interworking parts *
• Have cause to deviate from standards

* Not a necessary consequence of Proprietary Software, but since it isn't designed for interoperability it tends towards this