I am wondering whether legally a single patent with Claim A and Claim B allows the same legal protection for the content presented in Claim A and Claim B as two single patents containing in Patent 1 claim A and patent 2 Claim B?


There are multiple ways to end up with two patents with claims that cover related subject matter. One is by filing two applications and the other is by having a continuation or divisional from a single parent or some more complicated filing relationship using more than one continuation or divisional. In the case of two applications they might or might not be filed on the same day.

If filed as two applications there might or might not be an issue of double patenting depending on the exact subject claimed. The infringing product might infringe two claims neither of which is obvious in light of the other. This might be the case with two claims in one patent or in the case of two patents with one claims each. As mentioned in another answer there may be an issue of double patenting that was not caught by the examiner - if so a terminal disclaimer may be filed to obviate that issue.

If two claims in an original parent application are related but the examiner makes a restriction requirement (the claims are in different classes and it would be a burden to search both, for example) and the applicant does not traverse, then one claim can be pursued in the parent and the other claim can be refiled in a divisional. By the safe harbor (U.S.C. § 121) the claim in the divisional is by definition not subject to a double patenting problem. You end up with two patents of one claim each with zero double patenting issue.

The two cases have the same legal effect on the face of it. It is possible that scrutiny of the history of a patent prosecution may turn up some irregularity that can get a patent torn up. Two patents from two applications that have no formal relationship to each other might present a more difficulty target for invalidation. If the infringer was to use a USPTO process (IPR) to try to invalidate a patent it will cost more to try to invalidate two patents.

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This answer is with respect to US law and practice at the USPTO.

If claims A and B are obvious variations of one another, they should be part of the same patent. When such claims are submitted in separate patent applications, the later-filed application should be rejected on the basis of double patenting. Double patenting is the idea that the same invention, or obvious variations, should not be patented twice, because the patent term should not be extended by the filing of sequential patents and because the ownership of the same invention by two different entities would cause undue conflicts. The Applicant can respond by filing a terminal disclaimer in both applications. A terminal disclaimer is a statement by the patent owner to disclaim any time period of the second patent that extends beyond the expiration of the first patent. Also, the patents A and B must maintain common ownership.

The patent owner pays maintenance fees on both patents subject to a terminal disclaimer.

If claim A and claim B are in separate patents and are not subject to a terminal disclaimer, then on the face one assumes that they are separate and distinct inventions. They would provide different coverage for the different inventions. If they are found to be obvious variants, then the earlier-filed claims can invalidate (make obvious) the later-filed claims.

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  • This answer focuses on double patenting which is not really that important a factor to the core question. There are many ways to end up with a product infringing claims of more than one patent without the claims having a double patenting issue. One patent could be a lawnmower and a second to a self driving lawnmower. An infringers self driving lawnmower could infringe a claim from each patent with no issue at all of double patenting. If they do have a double patenting issue, as long as they as still commonly owned a terminal disclaimer can be filed. – George White May 26 at 22:51
  • With divisional practice the fundamental idea is to get two patents with related claims that are not subject to double patenting issues. Double patenting is a red herring in answering this question. – George White May 26 at 23:36
  • I interpreted the question as whether a single patent application having two distinct claims A and B could be split into two separate patent applications with the same claims A and B. In your example, if a single application claims to a lawnmower and a self-driving lawnmower, it should be subject to a restriction requirement because those claims are too different for a single patent application. – EA Kretzmer May 28 at 9:08
  • You are correct - I was talking about the more general case that is, I see now, not terribly relevant to the issue. – George White May 28 at 23:31

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