Open Source Vs Free Software
Those are, unfortunately, two terms that are used as they were synonyms, because the vast majority of Open Source Software is Free Software and viceversa, but they have a few key difference that reflect the different philosophies they come from. For example, a significant portion of the Privacy and Security community argues to only use Open Source Software, while meaning something completely different, and sometimes that something is Free Software.
The Definitions
Free Software
A program is free software if the program's users have the four essential freedoms:
- The freedom to run the program as you wish, for any purpose (freedom 0).
- The freedom to study how the program works, and change it so it does your computing as you wish (freedom 1). Access to the source code is a precondition for this.
- The freedom to redistribute copies so you can help others (freedom 2).
- The freedom to distribute copies of your modified versions to others (freedom 3). By doing this you can give the whole community a chance to benefit from your changes. Access to the source code is a precondition for this.
Open source Software
Introduction
Open source doesn't just mean access to the source code. The distribution terms of open-source software must comply with the following criteria:
1. Free Redistribution
The license shall not restrict any party from selling or giving away the software as a component of an aggregate software distribution containing programs from several different sources. The license shall not require a royalty or other fee for such sale.
2. Source Code
The program must include source code, and must allow distribution in source code as well as compiled form. Where some form of a product is not distributed with source code, there must be a well-publicized means of obtaining the source code for no more than a reasonable reproduction cost, preferably downloading via the Internet without charge. The source code must be the preferred form in which a programmer would modify the program. Deliberately obfuscated source code is not allowed. Intermediate forms such as the output of a preprocessor or translator are not allowed.
3. Derived Works
The license must allow modifications and derived works, and must allow them to be distributed under the same terms as the license of the original software.
4. Integrity of The Author's Source Code
The license may restrict source-code from being distributed in modified form only if the license allows the distribution of “patch files” with the source code for the purpose of modifying the program at build time. The license must explicitly permit distribution of software built from modified source code. The license may require derived works to carry a different name or version number from the original software.
5. No Discrimination Against Persons or Groups
The license must not discriminate against any person or group of persons.
6. No Discrimination Against Fields of Endeavor
The license must not restrict anyone from making use of the program in a specific field of endeavor. For example, it may not restrict the program from being used in a business, or from being used for genetic research.
7. Distribution of License
The rights attached to the program must apply to all to whom the program is redistributed without the need for execution of an additional license by those parties.
8. License Must Not Be Specific to a Product
The rights attached to the program must not depend on the program's being part of a particular software distribution. If the program is extracted from that distribution and used or distributed within the terms of the program's license, all parties to whom the program is redistributed should have the same rights as those that are granted in conjunction with the original software distribution.
9. License Must Not Restrict Other Software
The license must not place restrictions on other software that is distributed along with the licensed software. For example, the license must not insist that all other programs distributed on the same medium must be open-source software.
10. License Must Be Technology-Neutral
No provision of the license may be predicated on any individual technology or style of interface.
What's Different
The subject
With Free Software, the subject is always the user, which might be in the position of having to hire a programmer to fully exert the four freedoms, but everything begins and ends with the will of the user. Open Source Software, instead, does not have any focus on any subject in particular, if anything the definition of Open Source is just a list of requirements to make an Open Source license.
Freedom 0 vs Non-Discrimination of the license
This is probably the biggest difference between the two: for Free Software it's something so obvious that, the first time it was defined, this freedom wasn't included, but when it was added later, it wasn't as “Freedom 4”, but as “Freedom 0”: it's the premise to all the other freedoms. If the user cannot run the program in any way it desires for any purpose, it doesn't even make sense to begin to talk about the other freedoms, because are completely voided if this freedom isn't granted. One thing to note is that's a freedom, not an obligation: you're only free to use a software if you're also free not to use it. After all, what's the point of modifying the software you use if not to run your modified version instead of the “original”?
The closes thing to this in the Open Source definition is the principle of non-discrimination of the license (clauses 6 and 7), which simply says that an Open Source license has to not discriminate against a group of people or a field. While it is certainly a good thing, it's a far cry from the blanket grant to do anything that Freedom 0 provides, and it also only apply to the licenses, not the circumstances around them.
A clear example of violation of Freedom 0 via the circumstances around the license is tyrant devices: devices that forbid the user from installing an operating system other than what is specifically approved by the device's proprietor. It is not uncommon to see tyrant devices with key components of the preinstalled operating system being under a valid Free, Libre and Open Source license, but the user cannot choose to use any other operating system on it. While it still is Open Source because there's no discrimination happening, since the user cannot choose to not use that software, the Freedom 0 is not granted, therefore the license loses all meaning as a Free Software license, and the software itself is no longer Free.
More in general, while an Open Source license cannot forbid the use for a particular field, it can forbid a specific purpose, which is a violation of the Freedom 0, and the software can always be distributed with some Digital Restrictions Management (often erroneously called “Digital Rights Management”) while still abiding to the license, another violation of the Freedom 0.
To sum it up, Open Source does not generally believe in the Freedom 0, which, on the contrary, is the most important freedom for Free Software.
Freedom 3
While Freedom 0 is both the premise and the foundation of Free Software, Freedom 3 represents its culmination and modus operandi: once the user has improved a software, it can choose (it's a freedom, not an obligation) to publish its improved version, gratis or at a price. Once the fork exists, everyone, including the non-programmers, can benefit from it, and all the other versions of that program can copy the same improvements that that fork did. Thanks to this, with time, the community will decide in which direction the project is developed.
Open Source Software has the opposite principle: integrity of the author's source code. The author has the right to demand that no forks are made (to not confuse with the “fork and pull request to contribute”, which is a mere artifact of how Git-based forges operate), or at least for those forks to have a completely different name. Most “Open Source” developers choose to not enforce that right, because they recognize the usefulness of Freedom 3, but it's not always the case: for example, Mozilla, with its trademarks, forces everyone who wants to fork its projects to use a completely different name. This is because the modus operandi of Open Source is for everyone to come together and explicitly contribute to one and only one version of the project.
Free Software enthusiasts do often contribute to one big version of the project, but that's simply a path of least resistance: if what you have in mind is not some massive redesign, but a small objective improvement, rather than starting to maintain your own fork, it makes a lot more sense to get your improvements into the big version of the project and keep using that one once it accepts them.
Philosophy
This is where Open Source and Free Software diverge as much as humanly possible: Open Source isn't really a philosophy, it's little more than a development model based on the idea that, no matter what, there are more smart people willing to contribute to a project than the amount of people working for a specific company at any given moment, therefore, by making the source code public, independent developers will contribute to it making the software a lot better a lot faster than it would have ever been if the source code was secret. Open Source does not reject proprietary software, does not inherently reject malware (in fact, there have been several “Open Source” developers who intentionally put malware in their projects, one blatant example of it is so-called protestware), and does not even reject Closed Source software if not for being technically inferior for a specific use case.
Free Software, while it has naturally spawned the same development model as Open Source, it's much more than that, in fact there are several people who will tell you that Open Source is a conspiracy made by governments and big corporations to take advantage of the much more efficient Free Software's development model without having to recognize its ethical and political foundations, and those people might be right.
The fundamental idea of Free Software is that software has to provide freedom to the user, in other words, the user should be the ultimate arbiter of what the software is doing, not some proprietor who claims to know what's best for the user. This is a blanket rejection of all forms of malware, a.k.a. software designed to cause harm to the user, and more than that: Free Software automatically rejects all proprietary software as evil, because someone else other than the user is in control of the software, and of all Closed Source software because it's also proprietary software.
There is no “fitness for a use case”, “ease of use”, or any other argument in favor of proprietary software in the eyes of an exponent of the Free Software Movement: Free Software is the only kind of software that can grant freedom to the user, the best all the other kinds of software can do is the bare minimum of not having embedded malware, therefore Free Software is the only type of software worth using (for scopes other than reverse engineering that same software).