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The doctrine of claim differentiation states that every claim in a patent must be interpreted to have a different scope from every other claim in the patent. Thus, an independent claim must be interpreted as having a broader scope than its dependent claim(s). Let’s look at the chair example from chapter 1, and we will add a new set of claims 5, 6, and 7 to aid in illustrating the doctrine of claim differentiation.
1. A chair, comprising:
a seat having opposed upper and lower surfaces, the upper surface thereof being adapted for supporting the buttocks of a user;
a plurality of support legs, each said support leg having an upper end and a lower end, each said upper end thereof being mounted to the lower surface of said seat with each said support leg extending downwardly therefrom, each said lower end being adapted for removable positioning on a support surface; and
a backrest having opposed upper and lower ends, the lower ends thereof being secured to the upper surface of said seat, said backrest extending upwardly therefrom, whereby said chair may be removably transported by the user to the support surface for providing the user with temporary comfortable support.
2. The chair as recited in claim 1, wherein said seat has a substantially rectangular contour.
3. The chair as recited in claim 1, wherein said backrest comprises:
an inverted, substantially U-shaped frame having an upper portion and a pair of lower ends;
a plurality of vertically extending slats, each said vertically extending slat having an upper end and a lower end, the upper ends thereof being secured to an inner surface of said inverted, substantially U-shaped frame; and
a horizontally extending slat secured to, and extending between, the pair of lower ends of said inverted, substantially U-shaped frame, wherein the lower ends of said plurality of vertically extending slats are secured to said horizontally extending slat.
4. The chair as recited in claim 3, wherein the upper surface of said seat has a pair of recesses formed therein for receiving the pair of lower ends of said inverted, substantially U-shaped frame.
5. The chair as recited in claim 4, wherein each lower end of said inverted, substantially U-shaped frame has a substantially rectangular cross-sectional contour.
6. The chair as recited in claim 5, wherein each said recess has a substantially rectangular contour.
7. The chair as recited in claim 6, wherein each recess has a depth between approximately one-half of an inch and approximately one inch.
Claim 1 only limits the lower ends of the backrest to be secured to the seat. It does not say how this securement is performed. It is not until Claim 4 that the recesses are introduced. Since Claim 4 must have a different scope from Claim 1, under the doctrine of claim differentiation, this necessarily means that Claim 1 includes means of securement other than simple reception of the lower ends of the backrest within the recesses. It is important to note that this logical conclusion is accomplished without ever claiming what the other options may be, and without having to include the other choices in the drawings.
It is a fundamental principle of U.S. patent application drafting that whatever you claim must be shown in the drawings. If you claim a widget in a claim, then a widget must be shown in the drawings, otherwise, during prosecution, you must either amend the drawings (being careful not to insert new matter into the case) or cancel the claim(s) reciting the widget. Strategic use of the doctrine of claim differentiation allows a subtle way around this, though one must be very, very careful applying this principle. It is safer to actually show elements in the drawings rather than to rely on such legal strategy.
Note that Claim 7 defines an actual range in length measurement. This, by a similar logical analysis, means that Claim 6, from which Claim 7 depends, must be interpreted to have recesses with other depths outside of this range. It should be noted that claim differentiation only works with dependent claims.
Although claim differentiation appears to step on the toes of means-plus-function element interpretation, claim differentiation cannot be used to trump the statutory limitations on the scope of means-plus-function claims. The court in
Akos Sule et al.
v. Kloehn Co.1 held: “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, sixth paragraph, 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.”
2Footnotes — § 14.01.:
Given that twenty claims are allowed under the basic filing fee for a patent application, it is tempting to draft dependent claims that are not really necessary just to meet the twenty-claim limit. When drafting claims, you should keep in mind the actual purpose of a patent: to keep competitors out of the marketplace, or to at least make their entry into the marketplace much more difficult. In the chair example, you could easily write an entire set of dependent claims based on pure ornamental appearance rather than function. For example, one dependent claim could claim the seat as circular. The next could claim the seat as pentagonal. The next claim could claim the seat as hexagonal. The next claim could claim the seat as septagonal, and so on. Unless there’s a good reason for wanting to cover a particular shape or a certain dimensional range, then these claims are worthless, since just the broad “seat” in the independent claim already covers all of them.
It should be noted that sometimes, during prosecution, one must add a very narrow limitation in order to distinguish over the prior art. At that point, though, it is up to the inventor as to whether he or she really wants such a narrow claim scope.
Another issue is trying to list all possible options in a Markush-type dependent claim. For example, if an independent claim recites a connector, it will actually work against you to draft a dependent claim which includes every single type of connector you can think of. Why? Because the Examiner only needs to find one of those items on the list to reject the entire claim.
Target claiming is the strategy which has actually already been used in most examples throughout this book. In target claiming, one drafts a broad independent claim, and then drafts successively narrower dependent claims relative to a particular parameter. For example, let’s say that a claim set is drawn to a chemical method which includes heating. In the specification, it was described that the heating may take place above 100° C, but the optimal temperature occurs at 150° C.
Using target claiming, the broad independent claim will recite: “… applying heat at a temperature of at least 100° C … .” The first dependent claim may recite: “… wherein said step of heating includes application of temperature within the range of approximately 140° C and 160° C … .” The next dependent claim may read: “… wherein said step of heating includes application of temperature of approximately 150° C … .”
This is done not only to aid you during prosecution (the most broad range might read on the prior art, but the narrower you get, the more likely you will find your particular range or figure to be novel) but also give you broader coverage when it comes to infringement considerations. It is important to note that ranges, terms such as “approximately,” and so forth, must all be defined in the specification.
In the above example, let’s say that the invention is a new type of plastic, and one set of claims is drawn to the plastic composition itself, and the second set of claims is the method described above, including the step of heating at a particular temperature. Realistically, if your client is going to sue a competitor for infringement, which set of claims would be easier to take to court? If you are seeking enforcement of the plastic composition itself, that is something which you can easily see, hold in your hand, subject to laboratory testing, and wave in front of a jury. If you seek to enforce the method, how will you prove that the plastic was heated at 150° C and not, say, 165° C? Sure, you can do it, but it will take a lot of investigation, depositions, affidavits, and so forth during discovery.
Another common problem occurs when more than one party is required for infringement. For example, consider a method drawn to encryption and decryption of a signal. A single claim will have to include the method of encrypting the signal, transmitting the signal to someone else, and that other party then decrypting the signal. In order to show infringement, you now must have two accused infringing parties rather than one. To get around such a situation, if you can, you may try drafting one independent claim solely to a method of encryption, and then dependent claims to the additional steps of decryption, and then another set of claims vice versa.
A classic example of completely unenforceable claims (no matter how novel they may be) is shown in published patent application No. U.S. 2004/0093307 A1. The application claims a banking system in which a transaction takes place, at least in part, in a foreign country. The system cannot be enforced because U.S. patent law has no international reach.
1. A banking system comprising:
a first bank account directly owned by a first emerging local bank chartered in a first emerging market country;
a second bank account which is owned by a trust entity, wherein the emerging market bank is the beneficiary of the trust entity; and
wherein the first bank account and the second bank account are bank accounts at a first international correspondent bank.
