Description

 
		order for these freedoms to be real, they must be permanent and
irrevocable as long as you do nothing wrong; if the developer of the
software has the power to revoke the license, or retroactively change
its terms, without your doing anything wrong to give cause, the
software is not free. 

However, certain kinds of rules about the manner of distributing free
software are acceptable, when they don't conflict with the central
freedoms. For example, copyleft (very simply stated) is the rule that
when redistributing the program, you cannot add restrictions to deny
other people the central freedoms. This rule does not conflict with
the central freedoms; rather it protects them.