Why is the Apache license 2.0 patent license clause useful/important?

Question

I've read the Apache 2.0 license (A2L), in particular its clause regarding patent licensing (see below). I don't quite understand what's the use of it.

If Alice lets Bob use a piece of software under the terms of a permissive license without that clause - doesn't that already imply Bob has the right to " make, use, offer to sell, sell, import, and otherwise transfer the Work"? (I left out "have made", let's ignore retroactive considerations here.) That is covered by the license to "reproduce, prepare Derivative Works of, publicly display, publicly perform, sublicense, and distribute the Work and such Derivative Works in Source or Object form."

If the former is not covered by the latter, than - why not? And what could happen to Bob with the non-A2L license as opposed to the A2L?

PS - If it matters, suppose Alice and Bob do not live in the US.

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The relevant clause:

3. Grant of Patent License. Subject to the terms and conditions of this License, each Contributor hereby grants to You a perpetual, worldwide, non-exclusive, no-charge, royalty-free, irrevocable (except as stated in this section) patent license to make, have made, use, offer to sell, sell, import, and otherwise transfer the Work, where such license applies only to those patent claims licensable by such Contributor that are necessarily infringed by their Contribution(s) alone or by combination of their Contribution(s) with the Work to which such Contribution(s) was submitted. If You institute patent litigation against any entity (including a cross-claim or counterclaim in a lawsuit) alleging that the Work or a Contribution incorporated within the Work constitutes direct or contributory patent infringement, then any patent licenses granted to You under this License for that Work shall terminate as of the date such litigation is filed.

Answer 1

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.