(0) The freedom to run the program, for any purpose.
(1) The freedom to study how the program works, and change it to make it do what you wish. Access to the source code is a precondition for this.
(2) The freedom to redistribute copies so you can help your neighbor.
(3) The freedom to distribute copies of your modified versions to others. By doing this you can give the whole community a chance to benefit from your changes. Access to the source code is a precondition for this.
P.S. Странно, что не гуглилось: у меня ссылки выше выпадали в первой пятерке на запросы «free software four freedoms» и «спо четыре свободы» соответственно.
