Explicit is better than implicit. It is right that some have argued that the MIT and BSD licenses contain an implicit patent grant. However:
- These arguments have typically focussed on the US, leaving aside other legal systems that might be less open to finding far-reaching implied terms.
- AFAIK an implied patent grant is at this point a completely untested legal theory. In the future, the interpretation of whether the license terms include a patent grant will be for courts to decide.
- This leaves substantial uncertainty for both creators and users of open source software. Such FUD hurts the entire open source ecosystem.
- An implied patent grant may be revokable or limited. Without explicit license terms, this is simply not clear. Again, a court would have to decide what the implied terms are.
- As a worst case, an open source software could be a vehicle for a submarine patent that is only enforced after the software has found widespread use.
- The absence of clear terms gives power to bad actors that abuse their patents and thrive on the surrounding FUD.
For many open source projects, the presence or absence of a patent grant is absolutely irrelevant because no author holds any patents.
However, there are also a lot of open source projects that have institutional contributors from academia or industry, which do have a patent portfolio. The issue of patent licenses is much more urgent for those. The Apache Software Foundation has many such contributors in its projects, and therefore included suitable terms in its flagship license.
The Apache 2 License includes two sets of terms regarding patents:
- Contributors provide a patent grant to any of their patents that would be infringed by their contributions. Therefore, no bad actor can inject code and later claim that this infringes their patents.
- If anyone claims that the software infringes their patents, their patent license from (other) contributors ceases. This prevents bad actors from simultaneously enjoying the use of the software while trying to deny others the use. Furthermore, this offers some amount of legal shielding for contributors against claims by unrelated entities.
This explicit handling of patents makes the Apache License very attractive for the implementation of standards that require patent licenses. For example, consider a software that implements some patent-encumbered compression standard. Even if the patents are available under FRAND terms, this effectively excludes open source implementations. Arguably, an open source implementation might be fine but downstream users would be responsible for acquiring licenses (e.g. consider how Android patent licensing works: the hardware manufactorers are typically on the hook for acquiring patent licenses for the devices they sell to consumers).
However, if the patent holders come together to develop an open source reference implementation under the terms of the Apache 2 License, then it is safe to use that implementation for any purpose – while still allowing patent holders to enforce their patents against other implementations.