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The Average Joe’s Guide To Writing Patent Claims, Part 1

by | Mar 17, 2023 | 0 comments

A close-up image of a patent and a patent drawing.

Patent claims are the meat of a patent.

If you’ve been around the invention block a few times, you’ve undoubtedly heard the term “claims” thrown around as it relates to patents. You probably know that claims are a part of a patent application, and that they’re somehow important, but beyond that your knowledge might be a bit hazy. 

If that describes you, then you’re reading the perfect article to bring some clarity to this concept of patent claims. We’re going to give some easy-to-understand examples, and explain how utility patent claims are written to best protect the inventor, and you’ll even have a chance to write some basic claims yourself. 

It might sound daunting, but going through this exercise will help you more easily understand the claims your patent practitioner writes for your next patent application. And who knows, perhaps you’ll even be able to suggest some claims for them to get started?

When you hand a random patent to a patent agent or a patent attorney (we’ll just call them “practitioners” in this article), they will typically look first at the drawings and then flip to claim 1. Now if you’ve ever tried to read patent claims, which are listed in numeric order at the end of the patent document, they might seem a bit difficult to understand at first. Don’t worry, they are. 

So, why does the practitioner flip to claim 1 first? Simply because it is the most concise way to describe what that patent actually protects. If you only read the patent specification (all of the written part of the patent application apart from the claims), or just look at the drawings, you may get the impression that the patent protects a lot more than it does. But claim 1 defines the actual scope of protection that the patent affords the inventor, the protective boundary, if you will.  

I like to think of claim 1 as being a fence that encircles a property, in this case an intellectual property, where the “claim 1 fence” is the boundary of that property.  Subsequent claims will almost always be more restrictive, that is, they will be like a fence within the claim 1 fence that encircles less land. Perhaps claim 9 only encircles the Northwest quarter of the land, for example. Finally, when you get to the last claim, often claim 20, that fence might only protect a square yard… but of course if there’s gold under that one square yard, then it can still be a valuable claim. 

So, how do patent claims work? How is it that words can act like a fence to protect an intellectual property from trespassers, i.e., infringers? 

In the simple case of an apparatus claim, which is a claim that protects a product or a physical article of manufacture, a claim is basically a list of physical components and how they’re connected. For simplicity’s sake, let’s say the elements are A, B, and C. If you are granted a patent that lists elements ABC, and a competitor makes a similar product but adds element D (that is, he’s making ABCD), then he’s still making ABC and is infringing your patent. 

But if he is making ABD, then he’s not making element C and is therefore not infringing your ABC patent. This is an oversimplification, of course, but many people don’t realize that you have to subtract something from a claim to avoid infringing it, not add something to it. I cannot add a mirror to the back of an iPhone and then say that I can now make iPhones as long as they include mirrors. I would be infringing Apple’s iPhone patents, a sure way of meeting Apple’s intellectual property attorneys! 

When people ask if a competitor’s product is infringing their patent, I tell them to print a copy of their patent, flip to claim 1, and use a highlighter to highlight all of the nouns. If the offending product includes all of the highlighted nouns, and if those nouns are connected the same way as described in the claim, then it’s likely their patent is being infringed. 

But if the competitors product is missing one of those nouns, and instead of element C is using different element D, then it’s likely not infringing.  

Let’s use the example of a simple chair that has four legs, a horizontal seating surface, and an upwardly-projecting back support.  A very simple claim for such a device might read as follows:

1. A device for a person to sit upon, comprising: a seat having an upper surface, a lower surface, and an outer perimeter; four legs, each leg projecting downwards from the lower surface of the seat; and a back support projecting upwardly from the upper surface of the seat.

Notice that this claim is not even a complete sentence! (It might be helpful to add “What is claimed is:” in front of the claim to make it a complete sentence.)  Also, notice that when we first introduce an element, we use the articles “a” or “an,” and when we’re subsequently talking about the same element, we use the article “the.” Many practitioners use the article “said” but I prefer “the” for readability, but they mean the same thing… namely, we’re talking about the previously introduced element, not a new one.

Now, there are some problems with this claim, which we’ll get into shortly, but as you can see the elements ABC correspond to the seat, the legs, and the back support. The “person” is not considered part of the claimed invention since the person appears in the “preamble,” which reads “A device for a person to sit upon.” The claimed elements of the actual invention start after the word “comprising.” This is a claim that, if allowed by the Patent and Trademark Office (PTO), would protect a device that looks like this:

The Average Joe’s Guide To Writing Patent Claims, Part 1 fig 1

You might read this claim, just delivered to you by your patent practitioner, and think it’s pretty good. But wait! You need to put your competitor’s hat on and think about how to break this claim. Your smart competitor might come up with a product that looks like this, for example. Does this product infringe the above claim?

The Average Joe’s Guide To Writing Patent Claims, Part 1 fig 2

Or this product?

The Average Joe’s Guide To Writing Patent Claims, Part 1 fig 3

The answer to both questions is no. The three-legged chair, still perfectly capable of supporting a person above a ground surface, does not have four legs, but rather just three. Remember that in order to not infringe a claim you have to subtract something.  

Similarly, the stool without the back support does not infringe this claim either, as it only has elements AB, not ABC. Now it may well be that you don’t care about someone making the AB stool, since your ABC chair is clearly vastly superior to the stool and will have much greater market success. But what if your practitioner had written the following claims instead?

1. A device for a person to sit upon, comprising: a seat having an upper surface, a lower surface, and a peripheral edge; and at least three legs, each leg projecting downwards from the lower surface of the seat.

2. The device of claim 1 further including a back support projecting upwardly from the upper surface of the seat.

We changed “four legs” to “at least three legs” because a two-legged stool is unstable, and anything more than two legs will be stable and something we want to protect. We don’t really care if a competitor comes out with a two-legged unstable and unusable stool, and this claim protects what we actually do care about more than the first attempt.  

Here we’re introducing the idea of dependent claims. Notice claim 1 no longer claims the back support, and instead the back support first shows-up in dependent claim 2. Claim 2 depends on (the elements of) claim 1 in this example, since it starts out with “The device of claim 1 further including…” One way to read this is that claim 2 includes all of the elements of claim 1 (AB) and provides a further limitation of element C.  So claim 1 protects AB, and claim 2 protects ABC. 

If the PTO allowed claim 1 (AB), and by extension also claim 2 (ABC), now the three-legged chair and the stool with no back support would be covered by claim 1, and you’d be able to prevent a competitor from making, using, or selling AB and ABC products in the United States and its territories. (For simplicity we’ll just assume that we’re discussing United States patents.) So that would clearly be a valuable set of claims, with a particularly strong claim 1. 

In this example, if the PTO allows claim 1, they will automatically allow claim 2 since claim 2 includes all of the elements of claim 1, plus additional elements.  If claim 1 is allowable, so is claim 2 and any other claims that depend on claim 1.  That is to say, if AB is allowed, then ABC or even ABX will be allowed, too.  

In the next parts of this series…, we’ll keep trying to break these new claims 1 and 2, and provide you some more simple examples and even a chance at writing your own patent claims on a simple everyday invention.


  • Kevin Prince

    Kevin is an engineer (UC Berkeley, 1988), a Registered Patent Agent and owner of, author of The Art of the Patent, inventor, and co-founder of Inventor's Forum in 1990, a non-profit i...