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Doctrine of Claim Differentiation

Posted Monday, February 13, 2012 by Mike Gibbons

When drafting a patent application, the USPTO asks in MPEP 608.01(m) that the patent attorney or patent agent submit the claims beginning with the broadest subject matter, with subsequent dependent claims narrowing the subject matter further. (Read more about the structure of patent claims here.) In other words, an independent claim is the least restrictive, with dependent claims following the independent claim adding limitations to gradually narrow the scope of the independent patent claim.

Continuing a previous example, if we were seeking to patent a car, we might in our independent claim write “1. A motor vehicle comprising: a base; four wheels; and a frame for supporting a body.” A dependent claim could read “2. The motor vehicle of claim 1, wherein the body is black.”

Let’s assume for this example that claims 1 and 2 are allowed by the USPTO as they are written above. The doctrine of claim differentiation is a canon of interpretation that might be used in a patent infringement case. Recall from previous posts (such as this one and this one) that where there is ambiguity in a patent claim, and the issue of infringement turns on how the claim is interpreted, courts use various means of interpreting the claims.

Claim differentiation is a doctrine which tells us that if a dependent claim narrows subject matter from an allowed independent claim, then there must have been a reason for the difference in the two claims. Namely, that since the independent claim had a broader scope than the dependent claim, it must include possibilities other than what is claimed in the dependent claim.

Applying this to our car example from above, if the dependent claim limits the invention to a body of the car that is black, the doctrine of claim differentiation would tell us that the independent claim 1 must include other colors, even though the other colors are not positively recited in claim 1. Therefore, a green car wouldn’t infringe dependent claim 2, but the doctrine of claim differentiation would support a claim interpretation that a green car was implicitly claimed by claim 1.

Among canons of claim construction, the doctrine of claim differentiation is lower in priority than other canons. If there is a definition of a claim term in the specification, that is usually conclusive. In our car example above, if our specification disclosed that the car might come in colors including black, white, red and blue, and omitting green, a court is likely to find that the green car does not infringe.

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