Free software is not a subset of Open Source (page 40)More...
Reported on: 2005-12-13
In chapter 2. The Debian Project on page 40:
In chapter 2.2.2, Free Software is incorrectly described as a subset of Open Source: while it is true that there are there Open Source licenses which are not FSF-Free or not approved by Debian, that is a matter of interpretation, not of principles, as the Open Source Definition and the Debian Free Software Guidelines match almost word for word.
There are FSF-approved licenses that Debian-legal does not consider DFSG-free, and the book does not go to the extreme of saying that Debian-free is a subset of FSF-free.
Non-free Open Source licences: Indeed, the first version of the Apple Public Source License, which did not allow for private modifications of source (it forced disclosure of modifications even when these were not distributed), was approved by the OSI but not by the FSF, thus being Open Source but not free. So this much is true, but so it is with the GFDL.
Both definitions are synonymous in 99% of the cases, that and only clash in very exceptional pieces of software, being marginal cases. In fact Open Source and Free Software are philosophically different but functionally equivalent (key term: functional synonyms). Whether the motivation for the coders that write it is freedom or technical excellence, if some software is free it is almost certainly bound to be Open Source, and vice-versa.