What are the Four Freedoms of Free Software according to GNU?
The Four Freedoms — run, study, redistribute, improve — are the four rights software must grant its users to count as "free software."
They're numbered from 0 (a programmer's joke, counting from zero) and are deliberately ordered from least to most demanding of the developer:
| # | Freedom | Meaning |
|---|---|---|
| 0 | Run | Use the program for any purpose, no strings attached |
| 1 | Study | Examine and modify the source to suit your needs |
| 2 | Redistribute | Share exact copies with others |
| 3 | Improve | Share your modified versions too |
Key insight: Freedoms 1 and 3 are the ones with teeth, because they require the source code. You can't meaningfully study or improve a program you only have as a binary. This is precisely why "free software" implies "open source" — without the source, two of the four freedoms are impossible to exercise.
Important: None of this is about price. Free software can be sold for money; what the seller may not do is strip away these four freedoms from whoever receives it.
Mnemonic: "Run, Read, Redistribute, Rewrite."
Go deeper:
The Free Software Definition (GNU) — defines freedoms 0–3 (run, study, redistribute, improve) verbatim, including why numbering starts at 0.