Implicit patent licence
An implicit patent licence is a licence (grant of permission) created by the actions or words of an entity distributing software. Even if there is no licence explicitly saying you have the right to perform the ideas described in a patent, it is possible that the act of giving you the software included an implied promise not to sue you for using said software.
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Dan Ravicher's explanation
In 2005, Dan Ravicher explained[1] that, in the USA, recipients of software under the GNU GPL version 2 receive an implicied patent grant, based on the following US case law.
(Emphasis added by Dan.)
- De Forest Radio, 273 U.S. 236 (1927)
No formal granting of a license is necessar y in order to give it effect. Any language used by the owner of the patent, or any conduct on his part exhibited to another from which that other may properly infer that the owner consents to his use of the patent in making or using it, or selling it, upon which the o ther acts, constitutes a license.”
- Hewlett - Packard Co. v . Repeat - O-Type Stencil Mfg. Corp. , Inc., 123 F. 3d 1445 (Fed. Cir. 1997).
Generally, when a seller sells a product without restriction, it in effect promises the purchaser that in exchange for the price paid, it will not interfere wit h the purchaser's full enjoyment of the product purchased. The buyer has an implied license under any patents of the seller that dominate the product or any uses of the product to which the parties might reasonably contemplate the product will be put.
- Bottom Line Mgmt., Inc. v. Pan Man, Inc., 228 F. 3d 1352 (Fed. Cir. 2000)
Unless the parties provide otherwise, the purchaser of a patented article has an implied license not only to use and sell it, but also to repair it to enable it to function properly. This implied license covers both the original purchaser of the article and all subsequent purchasers.
In free software licences
In addition, it's possible that free software licences provide a stronger implied licence. Unlike licences for non-free software, which focus on listing what the recipient may not do, free software licences contain clear statements about what the user may do. This might mean that in addition to the act of distributing the software (which was sufficient for the above-mentioned rulings in the USA), the intent of the distributor can be read in the licence.
A very minimal example would be the MIT/X11 licence, which says: "Permission is hereby granted (...) to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so".
If this is shown to a judge, it would be difficult for the patent holder to argue that they never intended to give permission for the recipient to use or distribute the software. The MIT/X11 licence says it gives "permission" - not just "copyright permission".
A stronger example would be the GNU GPLv2. (See sections 6 and 7.)
Then finally there are licences such as Apache-2, MPL-2, and GPLv3 which contain explicit patent grants. People using this software should have no need of the implied licence.
