- The freedom to run the program for any purpose
- The freedom to study and modify the program
- The freedom to copy the program
- The freedom to redistribute modified or unmodified versions of the program
For numbers 2 and 4, access to the program's source code is necessary.
While the above criteria are met by public domain software (i.e., software that disclaims all copyright) which is released with source code , much of what is called free software is copyrighted and licensed, with the rights of copying, modifying and redistributing the software explictly given to the user. One free software license in particular, the GNU General Public License, or GPL, in addition to asserting the aforementioned rights, requires that all modified versions of the software must also be distributed under the GPL, which ensures that all modified versions also meet the above criteria.
Members of the Free Software Movement believe these freedoms should apply to all software, believing it is immoral to use force to prevent people from exercising these freedoms, or to provide software without providing the source. There is no consensus, however, how these aims should be met. Some believe that software should be freed through legislation; others through boycotts of proprietary software. Still others believe that time will tell, as free software will eventually be technically superior to proprietary software, and will win on the free market.
Supporters of Open Source argue for the pragmatic virtues of free software (aka "open source software") rather than questions of morality. Their basic disagreement with the Free Software Foundation is its blanket condemnation of proprietary software. There are many programmers who enjoy supporting and using free software but make their livings developing proprietary software, and do not consider their actions immoral.
Many members of the Free Software Movement believe similar rules should apply to all material currently subject to copyright and patent law, not just software.
Many English-speaking people in the free software movement have taken to using two Spanish words for "free", as the English language is ambiguous in this regard. One, libre, is equivalent to "unconstrained, with liberty". The other, gratis, is equivalent to "without monetary cost".