It is worth keeping mind that Freedom 0 can be denied to a greater extent than just preventing you from modifying the software. I first understood this when I

It is worth keeping mind that Freedom 0 can be denied to a greater extent than just preventing you from modifying the software. I first understood this when I was an undergrad, and my EE professors assigned us homework involving Matlab. The school had a license that allowed 50 concurrent users, and the software enforced that, which was a big problem when 80 students had homework to do. Yes, the freedom to modify the software would have allowed anyone to circumvent this restriction, but the inability to modify the software does not imply that such a restriction must exist. All of the four freedoms complement each other. In a world without Freedom 0, you might be denied the freedom to modify your software, because you might not be able to run the software needed to modify other software (e.g. imagine a simple world where all software is distributed as Python source, but where your text editor is designed to not be able to edit such source, and where your OS is designed to not run any other text editors -- modifying your software suddenly becomes much harder).