U.S. Patent Claims That Reference Other Claims: A Brief History
The claims in a patent define the limits of what the patent owner can prevent others from making, using, or selling. In U.S. patent practice claims of different scope are allowed, with one or more independent claims that define broad protection, usually in combination with dependent claims that refer back to one or more broader claims, and provide for narrower protection. But claims in U.S. patents have not always been this way. So, how did we get here?
Prior to 1836, the U.S. had a registration system for patents, rather than an examination system.[1] Under this system there was no set form for claims, and some patents had no claims at all. The Patent Act of 1836 instituted a requirement for an application to include at least one claim, but patent claims still had a variety of forms.
Still, with examination the form and content of the claims became the most important part of a patent application. But could a claim reference and incorporate the features of another claim? Some early claims did, but then along came an offhand remark in the convoluted 1873 case of Ex parte Sexton,[2] which was the basis for a decades-long Patent Office policy against claims that reference other claims.
Sexton was a petition for the extension of a reissue patent, one of a series of reissue patents (there were five in all). Claim 2 was the only claim that survived the reissue, and was recited as a “combination with the subject-matter of the first claim.” (Claim 1 had been found invalid because of prior art, and was to be disclaimed.) Most of what Acting Commissioner Thacher had to say about this situation was not problematic in any way:
The first claim here is invalid and must be disclaimed, yet it is part of the second, which is made up of both and is valid. This involves difficulty, or at least is somewhat awkward. It will of course have to be understood that the first claim of itself, as an independent claim, is stricken from the patent, but as connected with and embodied in the second it remains.[3]
The mischief came in a short sentence that proceeded this passage: “Each claim should be dawn complete in itself.” That statement became the basis for an Office policy that any claim that referenced another claim should be objected to on formal grounds, in essence that there should only be independent claims in issued patents.
This policy was finally changed in a 1917 case, Ex parte Brown.[4] Brown involved a petition to withdraw an objection to a dependent claim on formal grounds, with the examiner citing Sexton. Assistant Commissioner Clay, in deciding the case, dismissed as orbiter dicta the statement from Sexton regarding completeness of each claim. He found the claims at issue clear, with the dependent form helpful in highlighting the differences between claims. The examiner was instructed to withdraw the objections to the form of the dependent claims.
But Brown did not open the door to any and all dependent claims. Claims that depend in the alternative upon two or more other claims, what would be termed now multiple dependent claims, were disallowed in Ex parte Holst and Leers.[5] The rejection of such claims as indefinite was upheld as an extension of the practice against allowing alternative formulations in claims, and given that such formulations were too complex, and would require too much mental effort to parse.
Another limitation on dependent claims was set forth a few years later in Ex parte Hill,[6] which involved an application with a string of dependent claims, linked in a chain of dependencies. Two difficulties were cited in the opinion with the chain of dependencies – first, that such a chain would be confusing to follow (especially when the chained claims were not in sequence), and second, that amending such claims would require additional work, and would increase the chance of an error in the record. Thus it was “held that a dependent claim should depend from the combination of only a single other claim.”[7]
Brown, Holst, and Hill set forth the allowability of dependent claims, and the limitations on them, for the next two decades.[8] Change finally came in 1946, with a brief announcement by Commissioner Ooms that a chained series of dependent claims would be accepted, provided that “any series of dependent claims shall appear in the immediate consecutive order, and no dependent claim shall contain direct reference to more than one proceeding claim.”[9] Thus Hill’s prohibition of chains of dependent claims was set aside. This change of policy came in time to be incorporated into the first edition of the MPEP.[10]
A revision of the fee structure in 1965 provided an incentive for applicants to use dependent claims, with different fees being provided for the first time based on the number of independent and dependent claims.[11] At the time the basic filing fee paid for one independent claim and ten total claims, with additional independent claims requiring a fee of $10, and additional total claims requiring a fee of $2.[12] This encouraged the use of dependent claims, an incentive that has only grown bigger as the fees for additional claims have increased.[13]
Multiple dependent claims became permissible in U.S. practice in 1978, with the changes to 37 CFR 1.75(c) to accommodate multiple dependent claims being required for the U.S. to become a party to the Patent Cooperation Treaty. This did away with the prohibition on multiple dependent claims from Holst, although in U.S. practice a multiple dependent claim cannot be the basis for another multiple dependent claim. But the U.S. fee system is set up to discourage the use of multiple dependent claims, requiring a special additional multiple dependent claim fee,[14] and counting each claim referred to as a separate claim for fee purposes.[15]
There you have it -- that’s the story of how we got to the present situation in U.S. practice, with dependent claims permitted, even in chains or series of dependent claims, and with multiple dependent claims also permitted to a limited extent. The U.S. fee structure encourages the use of dependent claims, but in general strongly discourages multiple dependent claims.
[1] The Patent Act of 1790 did provide for examination of each patent application by three cabinet secretaries(!): the Secretary of State, the Secretary of War, and the Attorney General. Patent Act of 1790, Sect. 1, 1 Stat. 109. This unworkable system was replaced by a registration system with the passage of the Patent Act of 1793, 1 Stat. 318.[2] 1873 C.D. 66; 3 O.G.409.[3] 1873 C.D. at 73.[4] 1917 C.D. 22; 235 O.G. 1355.[5] 1918 C.D. 44; 253 O.G. 953.[6] 1924 C.D. 21; 319 O.G. 107. Hill, who represented himself before the Commissioner, was the same attorney who handled the Holst case six years earlier.[7] 1924 C.D. at 23. It is noteworthy that in Brown a chain of claims was accepted, with claim 2 referencing claim 1, and claim 3 referencing claim 2. See 1917 C.D. at 23 and 29.[8] See, e.g., Archie R. McCrady, Patent Law Practice: The Adjective Law Relating to the Prosecution of Applications Before the United States Patent Office 78 (2d ed. 1946) (citing Brown, Holst, and Hill); Emerson Stringham, Patent Claims: A Drafter’s Manual 999 (1941) (“The more recent American practice as to this style of claim [dependent claims or, as Stringham calls them, “subclaims”] will be found in the Brown, Holst, and Hill opinions.”).[9] 593 O.G. 431 (December 24, 1946) and 593 O.G. 575 (December 31, 1946) (both reproducing the Commissioner’s announcement of December 9, 1946).[10] See Manual of Patent Examining Procedure (MPEP) 608.01(n) (1st ed. 1949) (“a dependent claim may refer to a preceding dependent claim, which in turn refers to another preceding claim, thus a series of dependent claims … is permitted”).[11] Public Law 89-83, Section 1; 66 Stat. 796.[12] Can claims that reference other claims be independent claims? The short answer is “yes, at least for some purposes,” but that is a question better left for another piece.[13] The present fee structure provides an additional claim fee of $600 for each independent claim in excess of three, and $200 for each total claim in excess of twenty (large entity amounts).[14] Presently this fee for a large entity is $925.[15] Still, there are limited circumstances where it would be cheaper for an applicant to file a claim in multiple dependent form, but again we’ve reached an issue better left for another day.