Patent Claim Construction: Why Your Patent’s Scope Is Decided at Drafting
Before the fight about whether somebody infringes the claims of a patent, you have to first understand what those claims actually mean. This is referred to as “claim construction.” Lawyers often also refer to it as Markman.
In litigation, one of the first things the Court will do is decide what the words of the claim actually mean, and that decision frequently determines whether a patent is infringed, whether it is valid, and whether it is worth anything at all. Although the formal claim-construction process occurs during litigation (and usually in the courtroom), the outcome is shaped years earlier, during initial drafting of the patent application and during prosecution of that patent application.
Claim construction is usually highly disputed because it can shape the outcome of the litigation. Because of this, most discussions of claim construction focus on the courtroom: the briefing, the Markman hearing, and the dueling expert declarations. But that framing, while accurate, is incomplete. By the time a claim gets to the Markman hearing, its construction has already been shaped years earlier by decisions made during drafting and prosecution before the United States Patent and Trademark Office (USPTO). The words chosen, the definitions supplied, and the statements made to an Examiner all become part of the record that the attorneys will argue about and that the court will read.
NK Patent Law is a patent prosecution and intellectual property strategy boutique, and we draft and prosecute applications with this reality in mind. If you are weighing how your claims will be construed, call us at (919) 348-2194. For inventors and technology companies, the practical takeaway is that claim construction is not something that happens to your patent later in a vacuum.t It’s something you influence now.
This article explains how claim construction works, the evidence that is used, and why the most consequential claim construction decisions are made at the drafting stage.
Our attorneys hold engineering and science degrees and focus on patent prosecution and intellectual property strategy for technology-driven companies.
What claim construction is
Patent claims are the numbered sentences at the end of a patent that define the legal boundaries of the invention. You can think of them as defining the “fence” around your (intellectual) property. Everything that matters about a patent’s scope (the shape of the fence) comes down to how those claims are read.
Claim construction is the interpretation of that claim language. In federal court, claim construction is a question of law that is decided by the judge, not the jury. The Supreme Court established this division in Markman v. Westview Instruments, which is why claim construction is commonly called Markman. At the end of the process, the court issues a ruling that assigns meaning to the disputed claim terms, and the rest of the case, including infringement and often validity, is litigated against those constructions.
As a simple example, imagine a patent claim that says “part A is connected to part B.” The fight in claim construction may be about what does “connected to” mean? Does it mean “directly connected” such that part A must be immediately connected to part B? Or does it mean “indirectly connected” such that part A can be connected to part B through an intermediary part C? What if part A is detachable from part B, is that still “connected to”? There are endless examples and possibilities, but the overarching theme is to draw very clear boundaries around what specific words or phrases cover.
The governing standard for how courts construe claims comes from the Federal Circuit’s decision in Phillips v. AWH Corp. Under Phillips, claim terms are generally given their ordinary and customary meaning as understood by a person of ordinary skill in the art at the time of the invention, read in the context of the entire patent. The court does not interpret words in isolation, and it does not simply adopt a dictionary definition. It reads the claim against the patent’s own record.
That record is where drafting and prosecution decisions, which may have been 10+ years ago by the time claims are being construed, come back into play.
The evidence that governs construction
Courts construe claims using two categories of evidence, and they are not weighted equally.
Intrinsic evidence is the patent’s own record: the claims themselves, the specification (the written description and drawings), and the prosecution history (the file wrapper documenting the back-and-forth with the USPTO). This is what’s written in the four corners of the patent, along with the written back-and-forth that led to the patent being issued. Intrinsic evidence is the primary and most authoritative source for claim construction.
Extrinsic evidence is everything else: expert testimony, technical dictionaries, treatises, and the like. Courts may consult extrinsic evidence, but it is secondary and cannot be used to contradict the intrinsic record.
The significance of this hierarchy is hard to overstate. Two of the three sources of intrinsic evidence, the specification and the prosecution history, are created by the applicant and the applicant’s patent attorneys/agents during drafting and prosecution. Thus, the single most authoritative body of evidence a court will use to interpret your claims years from now is a document you are writing today. In that time, the industry will change, the technology will change, and the way terms are used will change.
Our attorneys hold engineering and science degrees and focus on patent prosecution and intellectual property strategy for technology-driven companies.
Call NK Patent Law at (919) 348-2194 or contact us online to discuss your patent strategy
The claims themselves: the first place to look
The first place to look for the definition of a claim term in a patent is the language of the claims themselves. As noted above, claim terms are generally given their ordinary and customary meaning. Sometimes this is clear from the claim language itself, and no further analysis is needed.
The specification: your patent’s reference guide
If further analysis is needed, the next place to look is the specification. Under Phillips, the specification is the single best guide to the meaning of a claim term.
An applicant is permitted to “act as their own lexicographer” in the specification, which means that you can define a claim term to mean something other than its ordinary meaning, as long as the definition is clear in the specification. Used deliberately, this lets a drafter lock in a favorable construction before any dispute arises. In theory, you could use this to say “within this patent, up means down” (however, just because you can, doesn’t always mean you should). For a more realistic example, going back to “part A is connected to part B” from above, you may choose to say in the specification that “Connected to refers to both direct and indirect connections, but it does not include detachable connections.” Again, whether you’d actually want to do this is a different question, but you can see how doing this could remove the later fight in court about what “connected to” means.
But the specification can also narrow a claim unintentionally. If the written description repeatedly describes the invention in terms of a single embodiment, a court may read the claims as limited to that embodiment, even when the claim language on its face appears broader. For example, if every reference to “connected to” in the specification says “directly connected to,” then a court may find that the claim term “connected to” should be construed to “directly connected to.” Describing the invention as “the present invention comprises” a specific structure, or disparaging alternatives, can permanently shrink the protection the claims would otherwise provide.
Drafting strategy for claim construction therefore involves more than writing broad claims. It involves writing a specification that supports those claims without inadvertently confining them, providing definitions where precision matters, and describing multiple embodiments so that no single one becomes the implied boundary of the invention.
This is also where the definiteness requirement of 35 U.S.C. § 112 comes into play. Claims must “particularly point out and distinctly claim” the subject matter of the invention. A claim term that cannot be construed with reasonable certainty can be held indefinite and invalid. Claim construction and validity under Section 112 are, in this sense, two views of the same drafting decisions. In other words, if the court can’t figure out how a term should be construed, it may find the claim invalid as indefinite.
Prosecution history estoppel: statements that follow the patent
The prosecution history is the second applicant-created source of intrinsic evidence, and it is often the most dangerous.
During examination, the USPTO will often reject the claims under various statutes, such as 35 U.S.C. § 102 (anticipation), 35 U.S.C. § 103 (obviousness), and, for software and other computer-implemented inventions, 35 U.S.C. § 101 (subject matter eligibility). To overcome these rejections, the applicant often amends the claims and argues that the claimed invention differs from the prior art in a particular way.
Those amendments and arguments become permanent. Under the doctrine of prosecution history estoppel, statements made to the Examiner can be used to limit how the resulting patent is later construed and enforced. An argument made to distinguish a single prior art reference can surrender claim scope the applicant never intended to give up, and that surrender can survive for the life of the patent. Going back to the earlier example, if the USPTO rejects your claim with a prior-art reference that shows that part A is indirectly connected to part B, and you argue in response that “Our claims are different because in our claims part A is directly connected to part B,” then you’re later going to be held to that, and your claim will be construed to require a direct connection.
In practice, this means a claim that looks broad on its face may be construed narrowly because of something the Applicant wrote in a response to an Office Action years earlier. The arguments that win allowance and the arguments that preserve enforceable scope are not always the same arguments, and a capable prosecutor weighs both at once.
This is one of the clearest reasons claim construction belongs in the prosecution conversation rather than only the litigation conversation. The estoppel is created at the USPTO. It is read by a court.
Means-plus-function claims and Section 112(f)
A specific claim-construction situation deserves its own mention. Under 35 U.S.C. § 112(f), a claim element drafted as a “means” for performing a function, without reciting sufficient structure, is construed in a particular and limited way: it is interpreted to cover only the corresponding structure described in the specification and its equivalents. For example, the claim term “a fastening means for securing the connection between part A and part B” will be construed as a means-plus-function claim. The means (“the fastening means”) performs the function (“securing the connection between part A and part B”). But the claim term itself doesn’t actually recite any structure. It simply says “anything that can secure the connection between part A and part B.” In this situation, this term will be construed to any structure that is described in the specification that secures the connection between part A and part B. If the specification only describes a bolt, then that term will be construed to only cover a bolt. If the specification describes a bolt, a screw, a nail, glue, and welding, then that term will be construed to cover all those things.
The consequence is that means-plus-function language does not capture every way of performing the recited function. It captures the structure the specification disclosed, and nothing broader. If the specification fails to disclose adequate structure, the claim can be held indefinite under Section 112. Courts also increasingly treat functional claim language using terms other than “means” as invoking Section 112(f), which can surprise applicants who believed they had avoided it. These other terms include things like “mechanism,” “module,” “device,” “component,” and “member.”
For mechanical, electrical, and software inventions alike, whether a claim is construed under Section 112(f) is a drafting decision with large downstream effects. It is best made on purpose, not discovered in litigation.
Why this matters even if you never go to court
Most patents are never litigated. Nevertheless, claim construction is still a major factor in those patents’ value, for several reasons.
Licensing and valuation depend on scope. A licensee, an acquirer, or an investor conducting patent due diligence will assess how broadly the claims can credibly be construed, and the prosecution history is part of that assessment. Claims that read broadly but were narrowed by prosecution arguments are worth less than they appear.
Freedom-to-operate and design-around analysis depend on scope. Competitors evaluating whether they can work around a patent are, in effect, performing their own claim construction. The clearer and better-supported the intrinsic record, the harder the patent is to design around.
Portfolio strategy depends on scope. Continuation practice, in which an applicant keeps an application family alive to pursue additional claims as products and markets evolve, lets a portfolio adapt to how claim construction and the competitive landscape develop over time. That option exists only if it is preserved during prosecution.
In every one of these settings, the question being asked is the claim construction question: what do these claims actually cover? The answer is set by the record built during prosecution, so it’s worth being intentional here.
How NK Patent Law approaches claim construction
At NK Patent Law, we treat claim construction as a prosecution discipline, not just a litigation event. We draft claims and specifications with an eye to how the intrinsic record will read to a future court, examiner, licensee, or competitor.
In practice, this means using the specification deliberately, supplying definitions where a term’s meaning should not be left to chance, and describing multiple embodiments so the claims are not implicitly confined to one. It means managing the prosecution history carefully, framing arguments to overcome rejections under Sections 101, 102, and 103 without surrendering more claim scope than necessary. And it means making conscious decisions about functional and means-plus-function language under Section 112(f) rather than leaving the construction to chance.
Our team combines this prosecution work with technical backgrounds in software, electrical engineering, semiconductors, biotechnology, chemistry, and mechanical engineering, because construing and drafting claims well requires understanding the technology, not just the law. We have also helped defend issued patents in post-grant proceedings, including Inter Partes Review before the Patent Trial and Appeal Board (PTAB) and Ex Parte Reexamination before the USPTO, where claim scope and the intrinsic record are tested in detail. That perspective informs how we build a record during prosecution in the first place.
We regularly help clients with:
- Drafting patent applications and claim sets built to hold up under construction
- Responding to USPTO office actions without surrendering unnecessary claim scope
- Structuring specifications and definitions to support the intended meaning of claim terms
- Evaluating claim scope against products, competitors, and freedom-to-operate questions
- Managing continuation strategy to preserve options as products and markets evolve
Our team has helped clients secure 2,100+ issued patents and 1,000+ registered trademarks, working with companies across 36 U.S. states and on international filings in 27 countries. Because patent law is federal, we represent clients regardless of where they are located.
NK Patent Law has been recognized by Legal 500 U.S. Elite, Best Lawyers in America for Intellectual Property, Business North Carolina Legal Elite, and the Chambers USA Regional Spotlight Guide.
Practical takeaways for inventors and companies
A few principles follow from how claim construction actually works:
- Treat the specification as evidence, not background. It is the primary source a court uses to construe your claims. Write it accordingly.
- Watch the prosecution history. Arguments and amendments made to win allowance can permanently narrow enforceable scope. Every Office Action response is a claim construction decision.
- Be intentional about functional language. Whether a limitation is construed under Section 112(f) should be a choice, not an accident.
- Preserve options through continuation strategy. Keeping an application family alive lets your claims adapt as products and competitors evolve.
- Involve technically fluent counsel early. The strongest claim construction outcomes come from prosecutors who understand both the technology and how the record will later be read.
Claim construction rewards work done early. The patent that holds up under scrutiny is usually the one that was drafted and prosecuted with that scrutiny in mind.
Speak with a patent attorney
If you are drafting a patent application, responding to an Office Action, or evaluating whether your existing claims will hold the scope you need, the decisions you make now will shape how your patent is construed later.
Call NK Patent Law at (919) 348-2194 or contact us online to discuss your patent strategy.