The following is intended to illustrate my question and is not a description of my idea, but it will express my concern.

Suppose someone has an active rock solid and un-contestable design AND utility patent or group of patents detailing a "shoe horn" with elaborate details on every possible way the "shoe horn" could be used -- BUT -- they overlooked one possible use. A "door stop". Can I patent and market a product that is in every way identical in size, shape, design, color and material, call it a "door stop" and market it as a "door stop? Or is that infringing?

(Boy, I hope I didn't just give away a great idea in my example and lose $20,000,000 on a stupid door stop.)

2 Answers 2


You may be able to patent a new use for an old thing, but you can't patent the thing itself unless it's somehow different from the old thing. What you may be able to do is patent the new method of use. For your example, you might be successful in claiming:

A method of preventing a door from closing, comprising:

inserting a shoe horn between a bottom of the door and a floor, thereby wedging the door in a fixed position.

(This is a crappy claim, and it may be invalid as a single-step method, but hopefully it communicates the idea.)

A method-of-use claim is often inferior to an article-of-manufacture claim, because you would have to sue each end user who buys a shoe horn and uses it to wedge open a door...you'd probably prefer to sue the manufacturer of shoe horns, or go to a retailer and seize all the shoe horns off their shelves. But if you really just have a new use for an old product, you probably don't have much choice.

An important part of designing patent claims is to consider, "who will make this device?" or "who will do the steps in this method?" That's the person who might infringe the patent, it's the person whom you might be able to sue, and from whom you might be able to collect damages or royalties. If it's an individual end user, it's likely that the cost of suing them will exceed the money you could recover from them, so that sort of claim may not be worth the cost of prosecuting it.


Freedom-to-operate opinions are always complex so you will absolutely need to consult with a real live patent attorney or agent to get an informed opinion. That said, given your hypothetical, you very well may be able to get a patent for the application of the patented device as a "door stop". This assumes there are no other patents with similar devices applied to door stops. In my experience, when you see a surprising gap in the claims, it often is due to prior art. Looking at the file wrapper of the patent in the US Public Pair (assuming its a US patent) is a good way to find out what limitations to claims were brought about during the examination process.

Your second question is whether you can market a product identical in every way to an existing product except applied to an alternative problem. In this case, there is no way to provide an opinion without actually analyzing the claims to the original patent and other relevant patents. Lets say someone invents the laser (assuming this is the first laser). You might invent a novel application of a laser. You get a patent on the new application, but might still require a license to make the laser. Also, there are other types of intellectual property than utility patents. The original device might be covered by a design patent which precludes you from marketing something that looks identical.

I am not an attorney, just an inventor with several patents. As I always do, I recommend consulting with a patent attorney.

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