(This question is closely related to Can I broaden the scope of a claim w.r.t. prior art through the use of "other than"?, in which I ask about patentability in case I have to compress all claims into a single independent claim.)

Let's assume there is a patent on a machine that "dries hair with hot air", and I have five other ideas how to dry hair (ice cubes, friction, whatever). I would like to avoid having to file five patents.

Obviously, I cannot claim a machine that "dries hair" any more.

When not restricting myself to one independent claim (e.g., at the USPTO), I would like to have a patent about machines that "dry hair by other means than hot air", with several independent claims claiming 1. a machines that "dries hair with ice cubes", 2. a machine that "dries hair with friction", etc. This seems possible from a point of view of writing the claims and filing the patent from a purely logistical standpoint.

However, would that still be a "unity invention"?

  • 1
    I'll let actual attorneys answer this question, but I can tell you from experience that the USPTO may make you split a patent into two if they think there is two different inventions in it.
    – Eric S
    Commented Jan 23, 2018 at 17:25
  • The answer depends on the jurisdiction. Which countries/regions are you interested in? Commented Jan 24, 2018 at 22:06
  • "Unity of invention" is a criteria used in most of the world. It actually has a definition. In the EPO it is "The requirement of unity of invention shall be fulfilled only when there is a technical relationship among those inventions involving one or more of the same or corresponding special technical features". In the U.S. the criteria for a valid restriction requirement is looser and more subjective. It can be driven by the examiner declaring that it would be an undue burden for them to search the multiple inventions or species of an invention they have identified.
    – George White
    Commented Jan 24, 2018 at 22:30
  • @chempatent1981 Mostly EPO and USPTO.
    – bers
    Commented Jan 25, 2018 at 8:57

1 Answer 1


In the EPO, a machine that dries hair with ice cubes and one that dries hair with friction would not be considered unitary. As mentioned in the comments by George White, the EPO looks for something that is "a single general inventive concept" (European Patent Convention, Article 82). In your example, you solve the problem of providing a machine that dries hair with two different solutions, one with ice cubes and one with friction. It really would not be fair if you had only one patent to pay and two "inventions" protected under it. To reverse the situation, if Apple had two new breakthrough ideas for touch screens that are manufactured by some novel ion-based nanomaterial and another one for touch screens manufacture by some novel polymer, would you consider it reasonable to have them both in one patent?

US is more liberal regarding the term of unity which is why US attorneys need EPO attorneys to file in Europe and vice versa. This relates to more delicate issues though. In your example, I do not think the USPTO would allow those two hair drying machine to be present in the same patent. At the end it is all about the payment a patent office receives about searching, examining and issuing your patent. They don't want to be paid once for two patents. US-based members might offer some additional info here.

  • "respond to the movement of the eye and another one wherein the screens respond to the tempo of breathing, would you consider it reasonable to have them both in one patent?" absolutely, "a screen responding to the biological signals of the user"
    – user18033
    Commented Jan 30, 2018 at 8:41
  • Ahh, ok you got me. I think still the EPO would not consider them unitary, you still have a point though. I will give another example and wait for objections ;) Commented Jan 30, 2018 at 9:17
  • @DonQuiKong to stay with your example and integrate the spirit of my question, consider "respond to human voice of the user" state of the art. The human voice clearly being a biological signal, would that change your judgement?
    – bers
    Commented Jan 30, 2018 at 9:24
  • 1
    @bers yes. I was about to write another comment concerning that. Unity isn't static, it changes with prior art because the inventive elements need to be unitable. For the touchscreen example "touch input" could be a uniting element, but the problem is having unity and novelty/inventiveness. So unity can change with the level of detail a claim needs to be inventive. Another example would be handheld-telephone-device which could totally include any kind of touchscreen devices and have unity.
    – user18033
    Commented Jan 30, 2018 at 9:31
  • @bers but another problem is, unity doesn't have a precise definition. If in doubt, just try it and split the application afterwards if necessary. For example, if you claimed the biological signal and during prosecution found out about the voice thing, chances are good the examiner would allow "biological signals specifically only eye movement and breathing speed" or something similar.
    – user18033
    Commented Jan 30, 2018 at 9:38

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