Brown & Michaels

Reading Claims for Infringement

First, we should say that infringement analysis is a matter for professional guidance for two reasons:

  1. Interpreting claims is a highly technical process, and should be done by a professional patent attorney based on the latest rules as laid out by the courts; and 
  2. If you have a formal written opinion in hand from a patent attorney which says you are not infringing a patent, you may be able to avoid added damages for "willful infringement" if you are sued. 

Therefore, the following is presented as a basic explanation of the process that an attorney would go through in analyzing a product for infringement of a patent, but should not be taken as legal advice of any kind. If you are reading this because you think you might be infringing a patent (or you think someone else might be infringing your patent) we strongly urge you to contact a patent attorney (preferably one at Brown & Michaels) immediately.

First Step - Look at the claims.
What do they mean, as properly interpreted ("construed")?

You will want to start by reading the claims - concentrate on the independent claims, since if you don't infringe the independent claims, you won't be infringing the dependent claims (which are narrower, by definition). 

The claim may not be formatted in a way which makes this analysis easy, so the first step is to pick it apart. List every element in the claims separately. Be sure you can identify each and every part and restriction which is described in the claim. The importance of this step cannot be overstated - every word counts. Suppose the claim says,

1. A widget comprising:

a solid cylindrical metal body having three circular ports arranged in a straight line along a length of the body; 


This means that an infringing product must have: 

(1) a body which is 
(2) solid, 
(3) cylindrical, and 
(4) metal, and the body must have
(5) exactly three ports which are 
(6) circular and 
(7) arranged in a straight line 
(8) along the length of the body. 

That's eight elements or restrictions out of only one brief clause, and every one is important. "Close enough" doesn't count - if your body is plastic, not metal, or it's hollow, not solid, or if you have two ports or five ports, or they're staggered instead of in a straight line, you don't infringe. (But see "doctrine of equivalents", below)

Look at the words which the patentee chose to describe these elements and restrictions - are any of them unclear, or capable of more than one meaning? You need to define every term before you go on to the next step. 

Plain Meaning vs. "A patentee is his own lexicographer": The terms in the claim should usually be given their ordinary meaning, but the courts have held that "a patentee is his own lexicographer". This means that, if the patentee chooses, he can invent a term or give a term a new or more restrictive meaning than would normally apply. If he chooses to do so, however, he needs to be clear in the specification about what the term means - for example: 

While the patentee may be his own lexicographer, he must be clear about what he's defining and may not invent a definition which contradicts the ordinary meaning or broadens it to the point of meaninglessness. For example, he cannot say "for the purposes of this patent, the term 'upward' includes 'downward", 'side to side' or any other possible movement", or "when this description says that the powder 'does not include water', this includes the situation where the powder does include water."  

Claim Differentiation: This principle says that there should be some difference between claims.  For example, look at the following claims:

1. A widget comprising a gronkheiser and a portoflan armature fastened to the gronkheiser by a movable connection. 

2. The widget of claim 1, in which the movable connection is a hinge. 

Since claim 2 says that the connection is a hinge, the principle of claim differentiation would indicate that therefore the term "movable connection" in claim 1 must include connections which are not hinges. Otherwise, there would be no difference between claim 1 and claim 2. This would be important if your product used a movable connection, but not a hinge. 

Extrinsic Evidence: There is some conflict between cases as to just how much weight is to be given to "extrinsic evidence" - that is, evidence as to the meaning of a term which comes from some source other than the patent itself. Sometimes courts will use dictionaries to define a term in a claim, sometimes they will refuse to do so. 

The most common extrinsic evidence is a dictionary definition. Of course, there are lots of dictionaries, and lots of definitions. It is best not to rely on an obscure dictionary definition to decide that your product does not infringe, if there is any argument that the context of the patent itself or industry usage would construe a term such that your product does infringe. 

Next, look at the Product...

The "All Elements Rule" - a very simple rule, which says that in order to infringe, a product must contain every single element in at least one claim of the patent. Look at each element in the claim, as properly construed in step one, and see if the product has it. If you can find even one element of the claim which is missing from the product, it does not infringe. 

Be very clear about this - the product must have every element in the claim, not that the claim must have every element in the product. A product may (and usually does) have other elements, but it still infringes if it has every one from the claim. 

Be sure to compare your product to the claims

Infringement is defined by the claims in the patent. The drawings and specification are often broader than the claims - the examination process often leads to narrowing of claims, and it is not unusual to have drawings which show an entire product where only a small part is claimed. It is quite possible that the application as filed showed something very similar to your product, but in the course of getting the patent, the patentee had to change the claims to give up coverage of your product. 

Often, a patentee will view his patent through the lens of what he is currently selling. His product is not necessarily what is defined by the claims in the patent. It is not at all unusual for a product to evolve beyond, and away from, the claims of an issued patent. Do not fall into the trap of comparing your product to his product, or allow the patentee to switch the subject to how much his product looks like yours. 

But wait - is the patent narrower than it seems? 

Prior Art: Take a very careful look at the patents and other art which was cited during the examination of the patent. By definition, the patent cannot cover anything which is taught by this "prior art" - and "taught" means shown in the drawings or described in the specification. The claims in prior art patents do not matter for this purpose.  

If your product is very close (or identical) to what is shown in one of the cited patents, it may be outside the scope of the claims even if a literal reading of the claims would indicate infringement. 

File Wrapper Estoppel/Disclaimer: Did the patentee say anything during the examination process which would affect the interpretation of the claims? 

You will need to get a copy of the "file wrapper" (prosecution history) for the patent. For very new patents, this may be available on the "Image File Wrapper" on the USPTO PAIR system. For an older patent you would have to buy a copy of the file history from the USPTO. 

Look at everything the patentee filed - especially the comments in every response to every office action, and in any Information Disclosure Statements (IDS). Also look at what the Examiner had to say in the office actions. Often, an applicant (or his attorney) may make statements in discussing the prior art citations which will change the meaning of terms in the claims, or which would act to exclude certain things from the claims either literally or under the Doctrine of Equivalents (see below). 

For example, suppose that the invention was a lug nut for automobile wheels which has large "wings" to allow it to be easily spun off by hand. The claim reads:

1. An improved lug nut for automobile wheels, comprising a body having a threaded interior for mating with a threaded stud on an automobile wheel, and a plurality of wings on an outside surface of the body for manual manipulation. 

Your product is a "knock-off" hub nut, which spins onto a special wide stud mounted at the center axis of specially-adapted wheels. Superficially, this claim might appear to describe your product. 

You look at the file history, and discover that the Examiner cited a 1962 MG catalog showing knock-off hubs. In order to overcome the reference, the applicant said "while the MG catalog shows a knock-off hub with wings, such hubs interacted with a shaft on the center of the wheel. In contrast, the lug nut of applicant's invention is threaded and sized to work with conventional studs on conventional automobile wheels, without the need for special hubs or fittings." 

By making that statement to get the patent, the patentee has removed your product from under the claim, since he has explicitly stated that his nuts must work with conventional studs without the special hub which your product requires. In other words, although your product does fit on a threaded stud, as the claim says, in his reply he has defined "threaded stud" in such a way as to limit them to just conventional wheel studs.  

Or, is the patent broader than it seems?
Infringement under the Doctrine of Equivalents

The "Doctrine of Equivalents" states that any element in a claim covers that which is literally claimed, and also equivalents of those elements. Over the years courts have struggled with just what this means, and how far the doctrine would extend coverage. 

The conventional definition of an "equivalent" is something which does the same thing in the same way to accomplish the same result. Clearly, a machine screw and a bolt are equivalents, since they differ only in size and whether the head is slotted or hex-shaped. A hinge and a rubber strip might be equivalents, but they might not - a hinge might be separable, and a rubber strip is not, for example. An incandescent light bulb and an LED might be the same if all that was needed is a light, but different if current drain or heat are issues. A different scope of equivalents is given if the element is closer to the point of the invention, or just a peripheral fastener or the like. 

In recent years the various Festo decisions, and other cases, have limited the scope of the Doctrine of Equivalents - in some cases eliminating it entirely if the claim was amended during prosecution to avoid prior art. This is all very legalistic and technical and not really an easy matter to determine. 

The bottom line is, if you think that your product might be infringing a claim under the Doctrine of Equivalents, you really need to get an experienced patent attorney involved.   

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Last updated: Tue, 10 Nov 2020