Once a provisional patent application has been filed, it cannot be amended (other than fixing procedural formalities). Therefore, to amend the subject matter one would need to refile the provisional patent application. As a reminder, provisional application is a temporary filing that holds your spot in a time based queue called the priority date, which, in case of provisional applications, is the filing date. This is the date the USPTO recognizes as your invention date. Provisional patent applications are held in confidence at the USPTO and are never published.
Another aspect to consider is that a provisional patent application should not incorporate the subject matter of another provisional application by reference. This means, one should not only present the changes in the new provisional, but refile the complete subject matter from the previous application as well.
Why a provisional application cannot be incorporated by reference?
37 CFR 1.57(d) states:
(d) “Essential material” may be incorporated by reference, but only by way of an incorporation by reference to a U.S. patent or U.S. patent application publication, which patent or patent application publication does not itself incorporate such essential material by reference. “Essential material” is material that is necessary to:
(1) Provide a written description of the claimed invention, and of the manner and process of making and using it, in such full, clear, concise, and exact terms as to enable any person skilled in the art to which it pertains, or with which it is most nearly connected, to make and use the same, and set forth the best mode contemplated by the inventor of carrying out the invention as required by 35 U.S.C. 112(a) ;
(2) Describe the claimed invention in terms that particularly point out and distinctly claim the invention as required by 35 U.S.C. 112(b) ;
(3) Describe the structure, material, or acts that correspond to a claimed means or step for performing a specified function as required by 35 U.S.C. 112(f) .
As stated, essential material needs to be referenced from a patent or a publication. However, since a provisional application never matures into a patent by itself and is never published, incorporating essential material from another provisional application is not possible.
To summarize: You cannot amend a provisional patent application, but may refile it. However, in doing so, you should not incorporate any material from the previous provisional filing by reference.
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