A friend directed me to a comment thread over at the Volokh Conspiracy, a blog I occasionally read and considerably respect. The response I ended up writing is substantial enough that I think it’s worth posting here.
I am the person who promulgated the term “open source”, and the senior founder of the OSI. As it happens, I’m also a semi-regular Volokh Conspiracy reader.
Alas, there is a fair amount of misinformation in this thread. Beginning with the misuse of “open source” to mean code with source that is available for inspection but not freely redistributable and modifiable; this is incorrect, and everyone who self-describes as an “open source” or “free software” programmer knows it’s incorrect. There is no universal term for accessible/non-redistributable/non-modifiable code, but I like to use “source under glass”.
“Open source” means code with a license that complies with the Open Source Definition (OSD). If you try launching a source-under-glass project on any of the community project-hosting sites such as SourceForge, Berlios, Alioth, gna, or Savannah, they will reject it. Even Microsoft — which is, to put it mildly, no friend of open source and would love to see the term neutered– recognizes the OSD as authoritative, having submitted licenses to OSI for approval.
As to whether “open source” and “free software” are synonymous: If you’re talking about software, the answer is “yes, for all practical purposes”; ever since Apple revised the APSL ten years ago, the exceptions have been minor and technical, involving licenses that are very little used.
Furthermore, there is no boundary in the developer community. No “open source” advocate refuses to work on “free software” projects, or vice-versa. RMS insists that the free software community is separate unto itself, but the actual behavior of hackers falsifies this claim.
If you’re talking developer philosophy, the difference is mainly one of marketing – what kind of arguments you use to evangelize to people who are not yet part of the community. “Free software” advocates tend to follow RMS’s lead and argue in a prescriptive, moralist vein. “Open source” advocates tend to follow my lead in arguing in a consequentialist, pragmatic way.
However, the situation is not quite as symmetrical as that might seem to imply. RMS claims (rightly) to be the founder and sole ideologue of “free software”. I make no corresponding claim; I consider myself part of a hacker tradition of open source that long predates “free software”, and only one of a collegium of leaders, theorists, and culture heroes which, in fact, *includes* RMS. I neither have nor want the normative authority over that larger tradition that he does over his faction, and in fact have spent a considerable amount of energy *avoiding* becoming the larger movement’s “indispensible man”.
RMS likes to maintain that there is an “open source” camp opposed to his “free software” movement. I think it is more accurate to describe his “free software” movement as a purist faction within the larger open-source community. This description better covers the actual working behavior of the people who self-describe with these labels.
In conclusion, I will note that the “open source”/”free software” distinction, to the extent it’s actually meaningful at all, matters a great deal more to the “free software” advocates than it does to the “open source” advocates. People outside the community may safely write it off as the standard sort of zealot-vs.-pragmatist hoo-hah that you see in reform movements of all kinds; as usual with such things, it is under most circumstances a dispute that can safely be ignored by everyone else.