A patent’s commercial value depends almost entirely on its claims—the numbered paragraphs at the end of the patent document that define, with legal precision, what the patent owner may prevent others from doing. A patent with broad, well-drafted claims can dominate an entire technology market. A patent with narrow or poorly drafted claims can be worked around by a competitor who makes even a minor design change. This article explains how claims work, how they are structured, and how courts interpret them in infringement cases.
The Legal Function of Claims
Article 70(1) of Japan’s Patent Act states: “The technical scope of a patented invention shall be determined based on the statements in the claims attached to the written application.” Article 70(2) adds that the specification and drawings may be consulted to interpret the meaning of terms used in the claims. This establishes a claim-centric system: protection extends to what is claimed, not to what is described in the specification or depicted in the drawings.
In the United States, 35 U.S.C. § 112(b) requires that claims “particularly point out and distinctly claim the subject matter which the inventor regards as the invention.” The Supreme Court’s Phillips v. AWH Corp. (415 F.3d 1303, Fed. Cir. 2005, en banc) established that claim terms are interpreted as understood by a person of ordinary skill in the art at the time of filing, using the specification as the primary intrinsic guide, supplemented by the prosecution history and, where needed, extrinsic evidence such as expert testimony and technical dictionaries.
Claim Structure: Independent and Dependent Claims
A patent typically contains multiple claims organized in a hierarchy. An independent claim stands alone and defines the broadest version of the protected invention. A dependent claim refers back to and incorporates all the limitations of an earlier claim, then adds further limitations to define a narrower version.
For example:
- Claim 1 (independent): “A device comprising elements A, B, and C.”
- Claim 2 (dependent on Claim 1): “The device of Claim 1, further comprising element D.”
- Claim 3 (dependent on Claim 1): “The device of Claim 1, wherein element B is configured to perform function X.”
This pyramid structure serves two strategic functions. First, the broad independent claim maximizes the scope of potential infringement catches. Second, the narrower dependent claims provide fallback protection: if the independent claim is found invalid, the dependent claims may survive as narrower but still valuable rights.
The “transitional phrase” in a claim—typically “comprising,” “consisting of,” or “consisting essentially of”—determines whether the claim is “open” or “closed.” “Comprising” (open-ended) means the claim covers embodiments that include the listed elements plus additional elements. “Consisting of” (closed) covers only embodiments with exactly the listed elements and nothing more. “Comprising” is far more common in utility patents because it captures a wider range of infringing products.
Claim Element Analysis: The All-Elements Rule
Patent infringement (literal infringement) requires that an accused product or method include every element of at least one claim. If even one element is absent from the accused embodiment, there is no literal infringement of that claim—this is the “all-elements rule” (or “all-limitations rule”).
To apply this rule, attorneys and courts decompose the claim into its individual elements and compare each against the corresponding feature of the accused product or process. This element-by-element mapping is the foundation of all patent infringement analysis.
Prosecution history estoppel limits the scope of claims: if, during prosecution, the applicant narrowed a claim by amendment or distinguished prior art in a written argument, the patentee may be estopped from recapturing that surrendered subject matter through the doctrine of equivalents. The US Supreme Court confirmed and refined this principle in Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co. (535 U.S. 722, 2002).
The Doctrine of Equivalents
Where literal infringement fails because the accused product differs from the claim language in some respect, the patent owner may still prevail under the doctrine of equivalents—if the differences are insubstantial. The classic US formulation, from Graver Tank & Mfg. Co. v. Linde Air Products Co. (339 U.S. 605, 1950), asks whether the accused element performs substantially the same function, in substantially the same way, to achieve substantially the same result as the claimed element (“function-way-result” test).
Japan’s Supreme Court recognized the doctrine of equivalents in the Ball Spline Bearing case (February 24, 1998), establishing five cumulative requirements:
- The differing portion is not an essential element of the patented invention;
- Even with the substitution, the same purpose is achieved and the same effect is obtained;
- The skilled person could have easily conceived of the substitution at the time of filing;
- The accused product is not identical to, or easily derivable from, prior art known at the time of filing; and
- The accused product was not intentionally excluded from the claims during prosecution (no prosecution history estoppel).
All five requirements must be satisfied; failure on any one forecloses a finding of equivalent infringement. The fifth requirement (no intentional exclusion) is particularly significant because amendments and arguments made during prosecution can permanently narrow the equivalents scope of the claims.
The Specification as a Lexicon
While the claims define the scope, the specification provides the context for interpreting claim language. A term defined explicitly in the specification carries that definition throughout the claims. A term used inconsistently in the specification may render a claim indefinite and therefore invalid.
The relationship between claims and specification creates an important drafting tension. A specification should be rich in disclosure—describing multiple embodiments, alternatives, and advantages—to enable broad claim language. But if the specification describes only a narrow embodiment of a term, courts may interpret that term narrowly in the claims even if broader coverage would otherwise be grammatically plausible. This “disclaimer” effect has been the subject of extensive US Federal Circuit litigation.
Claim Drafting Strategy
The fundamental trade-off in patent claims is breadth versus strength. A broad claim covers more competitive products and is more valuable if enforceable—but it is also more likely to be found invalid because broader claims more often overlap with prior art. A narrow claim is easier to maintain as valid but easier for competitors to design around.
Professional patent drafters address this trade-off through layered claim sets: the broadest independent claim captures the core inventive concept with minimal limitations; subsequent independent or dependent claims add progressively more detail. If the broadest claim is invalidated in litigation or an inter partes review, the narrower claims may survive and still provide meaningful protection.
Large technology companies routinely file patents with dozens or hundreds of claims. Under Japan’s fee schedule, the examination request fee scales with claim count—creating a financial incentive to consolidate claims while maintaining coverage breadth. Under US practice, claims in excess of 20 total (or 3 independent) also trigger additional fees.
The next article examines what happens when a patent is infringed—how infringement is determined, what remedies are available, and why most disputes settle before trial.
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