Claim Differentiation

There is also the doctrine of claim differentiation. That doctrine states that every claim in a patent must be interpreted to have different scope from every other claim. The effect is to force an independent (or parent dependent) claim to be read as having broader scope than its "child" dependent claim. This is readily appreciated by example. Consider once again the hypothetical chair claims discussed above:

1. A chair, comprising at least three legs, a seat, and a back, held together with at least one connector.

2. The chair of claim 1, having a fourth leg.

3. The chair of claim 1, wherein the at least one connector comprises a nail.

4. The chair of claim 1 wherein the at least one connector comprises a screw.

5. The chair of claim 4, in which the screw is at least 1" long.

6. A chair comprising a wooden frame supporting a seat and a back.

In claims 1, 4, and 5, the idea of the connector being a screw was introduced in claim 4. Since claim 4 must have a different scope from claim 1, this necessarily means that claim 1 includes connectors other than screws. That logical conclusion was accomplished without ever claiming what the other choices are, and without ever even including the other choices in the drawing. This can be a significant advantage because in general every claimed element that is susceptible to a drawing should have a drawing. Clever use of the doctrine of claim differentiation allows a patent attorney to inherently claim choices without ever having to draw them. Child claim 5 has a similar relationship to its parent, claim 4. Claim 5 recites that the screw is at least 1 inch long, which necessarily means that claim 4 must be interpreted to include screws having a length less than or equal to 1 inch. Note that claim differentiation only works with dependent claims.

Interestingly, the judicially developed doctrine of claim differentiation cannot be used to trump the statutory limitations on the scope of mean-plus-function and step-plus function claims. As explained by the District Court of NJ in 2001 , "A means-plus-function limitation is not made open-ended by the presence of another claim specifically claiming the disclosed structure which underlies the means clause or an equivalent of that structure. Indeed, the doctrine of claim differentiation cannot broaden claims beyond their correct scope, determined in light of the specification and the prosecution history and any relevant extrinsic evidence. Where the meaning of a term is clear based on the relevant intrinsic and extrinsic evidence, pursuant to 35 U.S.C. § 112 P 6, the doctrine of claim differentiation cannot alter that meaning. Claim differentiation is a guide, not a rigid rule. If a claim will bear only one interpretation, similarity will have to be tolerated. Under the circumstances the disputed claim will bear only one interpretation. Thus, in at least these specific instances, similarity with other non-asserted claims will have to be tolerated".