How to read a patent from top to bottom

A comprehensive look at a brief story of innovation

Patents have had a reputation of being mysterious documents, or at least very misunderstood. That’s why I was heartened to come across a blog post by Dan Shapiro that told the world how to read a patent in 60 seconds. Short answer: skip to the end and read the handful of numbered paragraphs called the “claims.” Each of these paragraphs defines exactly what the inventor says he or she invented—that is, what the inventor claims as the invention. Everything else is gravy.

Even though the patent’s title is “Mousetrap,” the inventor doesn’t claim to have invented a mousetrap. Skip to the paragraphs at the end, and you’ll see that the inventor actually claims a better mousetrap.

The story doesn't end there, though. It is impossible to completely, accurately, describe exactly what the invention is in a single English paragraph. Maybe the claim uses strange words that can only be understood in the context of the figures and examples. Maybe a word that has an apparent broad meaning is intended to describe only a more narrow aspect of technology. So take a quick look at the claims to get an idea, but to truly understand what the invention is you must go back and start at the beginning. This is not a reference manual for identifying the different elements as a patent. Rather, this is how you comprehend the patent as a whole.

The patent as a whole actually tells a tale of human innovation and ingenuity. Buried in a morass of what initially seems to be intractable legalese is a history of trial and tribulation, of failure, of discovery, and, ultimately, of enlightenment of the public of supposedly new-found knowledge. Maybe it is a grand story of the Wright Brother’s airplane, or the serendipitous story of VELCRO. Maybe the story is a load of b.s. You must be able to read this part of the patent—the gravy—to know one way or the other. That will take more than sixty seconds. And you need a guide. Let’s begin.

Our patent

We’re going to examine Volvo’s U.S. patent for the three-point safety belt, which issued in 1962.

Fun fact: In a convenient intersection of altruism and branding, Volvo essentially gave up its exclusive right to the new safety belt, letting other car manufacturers make cars with the same belt for free.

In a world…—the technical field

Right away, from the first word in the text, the inventor sets the stage:

We are talking about safety belts in vehicles. We’re mostly worried about cars here because that was the impetus to develop this idea, although maybe this would be useful in boats or airplanes too.

What everyone else been doingthe prior art

As mentioned above, the inventor did not invent the idea of safety belts even though the title of the patent is “Safety Belt.” He just claims to have invented a better safety belt. Fine then, but what other kinds of safety belts were people coming up with before the inventor charted a new path? More likely than not, the next thing that the patent does is give you some description of this in a section called the “Background of the Invention.”

Here, the inventor acknowledges that safety belts with shoulder straps, which are obliquely (diagonally) placed across the chest, were already known by others. Moreso, some people had already used a combination of shoulder straps and waist straps in their safety belts.

When the inventor is pushing the patent application through the patent office process, he or she, as well as his patent lawyer, must—by law—disclose examples of what they know to be in the prior art. The examiner reviewing the patent then performs an independent search to uncover other examples of prior art. In addition to what the inventor describes in this background section, the patent contains another section for the references that were produced during this process.

In prosecuting the Volvo patent, we can see that the inventor or the examiner apparently found six examples of related safety belts in various U.S. patents. These references are the full extent of what the examiner considered before ultimately becoming satisfied that the invention is new and not obvious, and issuing the patent.

Why everything else right now sucks right—the problems with the prior art

If the world already had safety belts with shoulder and lap straps, why does this inventor believe he created something new? Was there something wrong with the existing technology that sparked an idea? Was there a motivation to innovate?

Typically, the next thing a patent describes are problems with the current state of the art. The Volvo patent tells us:

Apparently, previous attempts at safety belts had serious ergonomic design issues that could harm the passenger, even if it kept the passenger from hitting the windshield. Or worse, there were structural issues that could cause a catastrophic failure of the harness system and launch the passenger—seat and all—out the windshield.

U.S. Patent 2,864,437, Safety Harness, by F.S. Spring

You can see what the inventor was talking about here by taking a quick look at the prior art that the examiner reviewed. For example, U.S. Patent No. 2,864,437 describes a three-point belt with a shoulder strap and lap belt. The top end of the shoulder strap is slung over and attached to the seat back. Common sense tells us that in a frontal collision, the energy of the passenger in motion will exert an overwhelming force that pulls the seat back forward. Since it was becoming commonplace for seat backs to recline, rather than serve as a rigid anchor of strength, these safety belt designs were ripe for improvement.

What I was trying to accomplishthe object of the invention

Unsatisfied with the status quo, the inventor then tells everyone what his goals were:

First, he wanted to take the seat out of the equation, so we could all sit on milk crates if we wanted to and still have a functioning safety belt. Second, he wanted to achieve this redesign in a way that would not sacrifice the protection the belt was supposed to provide.

TL;dr—the summary of the invention

The inventor now must quickly tell us the general idea of what his invention is in the “Summary of the Invention.” Although the inventor can throw all the nitty-gritty details of his engineering chef d’oeuvre in the patent application to tell the world of his exploits, only some of it may be what he considers to be his actual invention. In this section, he quickly puts down a rough sketch of the idea, which is supposed to lay out the full scope of what he will try to claim as his exclusive right.

You may notice later that this sounds pretty similar to the actual claims of the invention. They are supposed to be in harmony. But this text doesn’t have the ultimate legal power of defining what the invention is—only the numbered claims do that.

Here, the inventor gives us the highlights: the top of the strap is connected to the vehicle frame (i.e., not the seat back) near the shoulder, and a second point is mounted on the floor on the same side; furthermore, the strap is a single sling (i.e., rather than two) that is pulled across the body and is buckled to a floor mounting on the other side. Sound familiar?

With a little application of reading comprehension skills, we can now deduce what the meat of the invention really is. The prior art safety belts could break the seat back? Well, this invention mounts the belt only on the frame—not the seat. The prior art safety belts could cause spinal injuries? This invention uses a single strap connecting its three points, so it retains the passenger with uniform force.

Frame-only mounting, and a single strap that crosses both the shoulder and lap, are the two “points of novelty” of the invention

We’ve found the nucleus of the idea. The points of novelty. It may be that every other part described—like a detachable buckle—was already well known. But based on our read so far of the inventor’s story, using either of these two points of novelty in a safety belt device supposedly was not ever done before, despite many variations attempted.

You can use these points of novelty as a shorthand for talking about the patent. Does your safety belt have either of these features? If clearly not, you can tell your boss there is a good chance your company is not using this invention and in is the clear. Alternatively, if you happen to be knowledgeable about the safety belt industry, and feel confident that these features were used in a particular belt that the patent office examiner wasn’t aware of, you’ve gone a long way to show that this patent shouldn’t have issued because it isn’t anything new.

But remember, the claims are still the ultimate legal arbiter of what the invention is. It’s very convenient to tell people you live at the corner of Main Street and Elm Street when giving them directions to come visit. But according to your deed, you only own a very specific section of that dirt.

That said, sit down…this next part is going to take a whilethe embodiments

There are many policy considerations behind a patent system, and one of these goals is encouraging the public disclosure of ideas. In a competitive marketplace, there can be a tendency to keep innovations closed-source or trade secrets. So in return for a limited monopoly on an invention, the public gets to know of the invention, and more importantly, the inventor also teaches the public how to build the invention.

The next section of a patent is the “Detailed Description of the Invention.” Here, the inventor lays out, in great detail, how an example of the invention works. Well, she is supposed to anyways. This example, or embodiment, is supposed to be in “full, clear, concise, and exact terms as to enable any person skilled in the art or science to which the invention or discovery appertains…to make and use the same.” In some patents, this detailed description may be dozens of pages of text and dozens of figures, or more!

The text usually refers to figures and drawings throughout to help explain. Elements in the figures are identified by name and a unique number, like “pintle 18” or “latching lever 17.” In the Volvo patent, the inventor provided three figures and one example embodiment of the safety belt.

In Figure 2, you can see the single length of strap 7 and 8, and the three mounting points of the invention—the two floor mounts 3 and 4, and the top body mount 5:

Figure 2

Because the patent is intended for someone skilled in the art and not jut anyone off the street, it probably glosses over a few details you or I may not understand. Maybe you’ve never heard of a “pindle”? Or a “knurled pin”? That’s ok, so long as a mechanical or automotive engineer gets it, or at least could quickly look it up in in the index of one of their engineering texts.

The Volvo patent describes a mechanical device. If the invention was a process, like how to manufacture Gore-Tex, the description should sufficiently describe the steps of the method. If the invention was software, the components and their functions must be fully described. Source code or pseudo-code is not necessary, since someone skilled in the art (e.g., a programmer) should be competent enough to create a program from scratch if given only the functional requirements.

“What I claim…”—the claims

With all of that behind us—the state of the art, its problems, the inventor’s goals, and a description of the invention—now, and only now, are we in a position to accurately understand what the inventor claimed as the invention. In fact, reading the claims in the context of the entire patent document is exactly what patent law says you should do.

The claims are are at the end of the text, conveniently identified because they are prefaced with something like “What I claim is.”

Each numbered claim is a separate, distinct claim for an invention. There usually are several claims (sometimes dozens or hundreds), each a different variation on the invention. Think of each patent claim as land claim in a deed filed at the county register’s office. It stakes out the boundaries of a specific implementation of an idea. Make a device or use a process that is exactly the same as what the claim says, and you have made or used the invention.

The Volvo patent has two claims, an independent claim and a dependent claim. Let’s look at the independent claim, Claim 1, first:

Claim 1

This looks pretty similar to the summary of the invention we examined earlier. As highlighted, you can see it includes one of the two points of novelty discussed earlier: mounting the safety belt to the vehicle frame at two points.

There are many other parts, or elements, to this claim. Every single one of them is a necessary part of the claimed invention and cannot be ignored. If a device lacks even one element, it is not the same as this invention. It does not infringe the patent claim. Or, on the flip side, a device in the prior art missing any one element doesn’t immediately tell us the invention is not something new.

Note, however, that this claim doesn’t include the second point of novelty: the single strap that crosses both the shoulder and lap. Here, the inventor (and patent examiner) thought that the frame-only mounting was novel enough to warrant its protection on its own terms.

What about the single-belt idea? That’s where the “dependent” claim, Claim 2 comes in:

Claim 2

You can see this claim begins with “A safety belt defined in claim 1….” That means that the inventor is claiming an invention including everything described in Claim 1, plus additional elements. In Claim 2, we see that the inventor now adds in the second point of novelty, because this claim describes that the shoulder and lap belts are made from a continuous length of strap.


In barely three pages, one of which is just drawings, the Volvo patent has told us a story of innovation. Understanding the story being told helps us identify whether the inventor is a genius or a charlatan, or whether the invention is a true advancement of technology or just another variety of snake oil.

There is a lot of criticism directed at the U.S. patent system today, but a lot of misunderstanding of what a patent is leads to misdirected anger rather than constructive solutions to real problems. Hopefully, the picture is a little more clear now.

Technology and the patent system have changed much since the Volvo patent in 1963. In future articles, I aim to discuss the various issues raised by the intersection of patents and the modern information economy.

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