The four essential freedoms

A computer program is considered free software when users have these four essential freedoms:

Freedom 0: The freedom to run the program as you wish, for any purpose.

Freedom 1: The freedom to study how the program works, and change it so it does your computing as you wish. (Requires access to the source code.)

Freedom 2: The freedom to redistribute copies so you can help others.

Freedom 3: The freedom to distribute copies of your modified versions to others, giving whole community a chance to benefit from your changes. (Requires access to the source code.)

Some history:

• Around 1990, there were only three freedoms (1, 2, and 3).

• Freedom 0 was added later:

  • Open source advocates realized a need to mention running the program freely for any purpose.

  • This seemed more basic than the other freedoms, so it was added before them as “freedom 0.”