When two or more persons make an invention, they are considered by the United States Patent and Trademark Office (USPTO) to be joint inventors. Inventors may still be considered joint inventors even though they did not physically work together, work at the same time, did not make the same level of contribution to the claims, or contributed to the subject matter in each claim in the patent application.
Inventorship in a patent is based on the claims; however, in instances where an application is filed without claims (e.g., provisional application), each inventor named in the provisional application must have contributed to the subject matter that has been disclosed in the application.
When the claim(s) in a pending patent application are amended, if one or more joint inventors are no longer considered to be inventors of the subject matter contained within the newly amended claim(s) then the application must be amended to remove the inventor or joint inventors that are no longer contributing to the claims.
Likewise, if an amendment to the claims adds subjecter matter that was invented by a joint inventor not named in the application, the application must be amended to include the joint inventor.