The four freedoms

  1. The freedom to use the software for any purpose.
  2. The freedom to study and improve the software.
  3. The freedom to share the software.
  4. The freedom to collaborate on the software.

Let’s examine each of the four freedoms in more detail.

0: Use the software

The “zeroth” freedom guarantees the right for everyone to use the software for any purpose. You are entitled to the use of any free software for any purpose, including commercial use – counter-intuitively, you can sell free software. You can also incorporate free software into your own work, but be careful – there are some gotchas here, which we cover under use & reuse.

In free software lingo, this is often called the “non-discrimination” requirement.

1: Study and improve the software

The first freedom guarantees the right to study the program’s behavior. You have a right to understand how the software you depend on works! In order to facilitate this, the source code must be included with the software. The publishers of free software cannot obfuscate the source code, forbid reverse engineering, or otherwise prevent you from making use of it.

Moreover, you have a right to improve the source code. You are not only given the right to read the source code of free software, but also to change it to better suit your needs.

2: Share the software

The second freedom guarantees the right to share free software with others. If you have a copy of some free software, you can give it to your friends, or publish it on your website, or bundle it with other software and share it as part of something bigger. You can also share your improvements to it – then it’s better for everyone!

You can charge a fee to those you share the software with, for instance to cover the costs of bandwidth. Note however that the recipient is entitled to the right to share it themselves, without paying back any royalties.

3: Collaborate on the software

The third freedom guarantees one additional right: the right to collaborate with others on improving the software. You can study, improve, and share the source code, and the people you share it with can study, improve, and share it right back with you. This is the foundation of the free software movement: a global community of software enthusiasts sharing and improving software together.

Next: Free software licenses