If I manufacture A+B+C, then I would be infringing upon A+B, no?

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    How could the patent to A+B not be invalid due to prior art?
    – SJuan76
    Commented Sep 9, 2022 at 18:02
  • 2
    Your example lacks enough coherent detail for a reasonable answer. Please provide a specific example. Commented Sep 9, 2022 at 18:29
  • 1
    It seems as though you are indicating that "A+B" is a subset of "A+B+C". If that's the case then "A+B" could not be patented by someone else since it's obviously already patented. If someone were to be granted such a patent, then you could easily challenge it. For example, if I patent a pencil as consisting of a wood body, a graphite lead, a rubber eraser, with a metal barrel connecting it together, a new patent application for a wood body with a graphite lead core should be rejected since it's nothing but a subset of a previously patented device.
    – jwh20
    Commented Sep 9, 2022 at 18:53
  • A+B turns out to be a better solution than A+B+C. C turns out to be superfluous complexity. Commented Sep 9, 2022 at 18:55
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    @BigCatPublicSafetyAct it's a better solution, but it's not a new invention. It's just a new way of using an existing invention after removing one of its parts. It's therefore not patentable. The A+B patent, if it was granted, is invalid.
    – phoog
    Commented Sep 9, 2022 at 19:41

3 Answers 3


What the discussion has missed is that how elements are interconnected and interrelated is itself an element. If A and B are things, some C must define their interrelationships.

Image a 4-wheel car exists and what everyone knows is that to be stable a car needs 4 wheels in a rectangular arrangement.

Someone invents a 3-wheel car by realizing stabilization can be achieved by only one rear wheel if it’s located between the front two.

The four wheel car had three wheels but it isn’t a 3-wheeled car. The claim for the 3 wheeled invention needs to not say a car having 3-wheels. That already exists. But a car balanced as a working 3-wheeled car could be claimed.

So A + B + C + D existed but someone figured out how to make a workable A + B + C and has a patentable invention. The seeming contradiction is solved by noting that the first case was really A,B,C,D and X where X defines the relationship between the first four elements. The new invention has A,B,C and Y. It is novel and not a subset of the prior art.


That depends a bit on how exactly the patents came about and are written

  1. If you have A+B+C, everyone can do just A+B without infringing
  2. A+B is unlikely to be granted since it's included in A+B+C so there is prior art
  3. Someone might be able to patent A+B+NOT_C where "NOT_C" is new the invention. That's still unlikely to get granted, but may happen in rare cases if NOT_C is really non-obvious and everyone has been doing +C since the dawn of time.
  4. If that happens you can still keep manufacturing using A+B+C. You would not be able to do A+B without doing C as well.

The most likely outcome here that everyone (including you) will just use A+B with no one owning a patent on it.

  • Are you assuming a first-to-file regime? Or a first-to-invent regime?
    – user46677
    Commented Sep 10, 2022 at 13:52
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    @user133469 First-to-invent is no longer a thing: the US is First to File since 2013! - Technically it's First Inventor to File, but still: whoever files first wins the patent.
    – Trish
    Commented Sep 10, 2022 at 14:30
  • @Trish thank you!
    – user46677
    Commented Sep 10, 2022 at 15:05
  • If your invention used A, B and C because A and B alone didn’t work, then the new patent will be for using A, B, plus some very non-obvious trick to make them work without needing C.
    – gnasher729
    Commented Sep 12, 2022 at 6:27

Assume that neither of A, B and C is patentable (because they don’t anything useful on their own), and combining them was not obvious which is why you could get a patent.

A and B together don’t work, at least not if combined in an obvious way, or if combined in the way you did if we left C out. So I can’t get a patent for A and B because it doesn’t work.

But I could get a patent for combining A and B in a new non-obvious way. Your invention is not affected because it doesn’t combine A and B that way. On the other hand, your invention is not prior art assuming A and B each were not patentable.

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