What is literal patent infringement?
Literal patent infringement occurs when an accused product or process contains every element of a patent claim exactly as written, with no missing elements. It follows that if even one element of the claim is absent from the accused product or process, there is no literal infringement of that claim.
The statutory foundation
Patent infringement is governed by 35 U.S.C. § 271(a), which provides that whoever without authority makes, uses, offers to sell, or sells any patented invention within the United States, or imports any patented invention into the United States during the term of the patent therefor, infringes the patent. Each act listed in § 271(a) is independently actionable: a party who manufactures a patented product without authorization infringes even if no sale ever occurs, and importing or offering to sell are each separately covered.
The two-step analysis
Courts evaluate literal infringement in two steps: first construe the claim language, then compare each construed element against the accused product or process.
Step 1: Claim construction
Before comparing a claim to an accused product, a court must determine what each claim element means. In Markman v. Westview Instruments, Inc., 517 U.S. 370 (1996), the Supreme Court held that the construction of a patent, including terms of art within its claims, is exclusively within the province of the court. In practice, this takes the form of a Markman hearing, a pretrial proceeding at which the district court resolves disputed claim terms before the case proceeds to trial or summary judgment. Parties submit competing proposed constructions and may present expert testimony; the court issues a claim construction order that governs the rest of the litigation.
Step 2: Comparison to the accused product
Once the court has construed the claim, each element of the construed claim is compared against the corresponding features of the accused product or process. Determining whether an accused product or process infringes a claim as construed is a question of fact for the jury.
The division between these two steps has strategic consequence. A favorable claim construction ruling for a defendant can eliminate infringement exposure without any disputed facts about the product itself. Conversely, a patentee who secures a broad construction may find infringement almost certain as a factual matter.
Claim construction under Phillips
The meaning assigned to each claim element in Step 1 determines the outcome of the literal comparison in Step 2. Under Phillips v. AWH Corp., 415 F.3d 1303 (Fed. Cir. 2005) (en banc), claim terms receive 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 including the specification.
Intrinsic evidence, consisting of the claims themselves, the specification, and the prosecution history, is the primary and most reliable source for determining the meaning of claim terms. Extrinsic evidence, including expert testimony and technical dictionaries, may help a court understand the relevant technology but cannot override what the patent's own intrinsic record establishes.
Two doctrines can override the ordinary-meaning result. A patent applicant may act as a lexicographer by defining a claim term in the specification with reasonable clarity, deliberateness, and precision, overriding the term's ordinary meaning. Clear and unmistakable disavowal of subject matter in the specification or prosecution history narrows the scope of a claim beyond what the literal claim language would otherwise suggest; ambiguous statements do not suffice.
The all-elements rule
The core requirement for literal infringement is the all-elements rule. In Warner-Jenkinson Co. v. Hilton Davis Chemical Co., 520 U.S. 17 (1997), the Supreme Court held that each element contained in a patent claim is deemed material to defining the scope of the patented invention, and the doctrine of equivalents must be applied to individual elements of the claim rather than to the invention as a whole.
Applied to literal infringement, this means every limitation of the asserted claim must be found verbatim in the accused product or process. A product that satisfies nineteen out of twenty claim elements does not literally infringe that claim. The comparison is element by element, not an overall assessment of similarity to the claimed invention.
How transitional language shapes the comparison
The transitional phrase connecting a claim's preamble to its body controls whether unrecited elements in the accused product affect the literal infringement determination.
"Comprising" is inclusive and open-ended: it does not exclude additional, unrecited elements or method steps beyond those named in the claim. A product that contains all recited elements plus additional components still literally infringes a "comprising" claim; the extra components are irrelevant to the comparison.
"Consisting of" is closed: it excludes any element, step, or ingredient not specifically recited in the claim. A product that adds an unrecited component beyond those named in a "consisting of" claim does not literally infringe that claim.
This distinction matters for design-around analysis. A strategy of adding extra components to a product defeats a "consisting of" claim but does not defeat a "comprising" claim if all recited elements remain present.
When literal infringement fails: the doctrine of equivalents
When one or more claim elements are absent from the accused product, there is no literal infringement. In that situation, a patentee may pursue infringement under the doctrine of equivalents. If an accused product or process does not literally infringe a patent claim, it may still be found to infringe under the doctrine of equivalents, which asks whether the accused product performs substantially the same function in substantially the same way to obtain substantially the same result as the claimed element.
The doctrine of equivalents is bounded by prosecution history estoppel. Prosecution history estoppel gives rise to a rebuttable presumption that a patentee has surrendered, and cannot recapture through the doctrine of equivalents, the claim scope given up by a narrowing amendment made during prosecution, a presumption the patentee may overcome only in limited circumstances. When a patentee narrows a claim during prosecution to overcome a rejection, the surrendered subject matter generally cannot be recovered through an equivalents argument unless the patentee rebuts that presumption.
Literal infringement at a glance
| Step | Question | Who decides |
|---|---|---|
| Claim construction | What does each claim element mean? | Judge (question of law) |
| Comparison | Is every element present in the accused product? | Jury (question of fact) |
| Transitional phrase | Effect when accused product adds extra, unrecited elements |
|---|---|
| Comprising | Extra elements do not defeat literal infringement |
| Consisting of | Extra elements defeat literal infringement |
Practical notes
- Analyze each claim separately. A patent may have many claims; an accused product might literally infringe some and not others. The all-elements test is applied claim by claim, element by element. Identify which claims are at issue before investing in a full product comparison.
- Claim construction drives the outcome. The element-by-element comparison depends entirely on how each term is construed. A broad construction may bring the accused product within the claim's scope; a narrow one may exclude it. Treat the Markman hearing as the pivotal event it is.
- One missing element defeats literal infringement. Defendants should identify the claim element least likely to read on the accused product. Plaintiffs should confirm every element maps before filing or asserting infringement. A claim chart, element by element, is the standard tool for both sides.
- Check the doctrine of equivalents as a second layer. When literal infringement is absent because of a missing or substituted element, ask whether a substantial equivalent is present, then check whether prosecution history estoppel forecloses that argument.
- Transitional language determines the significance of extra components. Adding components to a product will not avoid a "comprising" claim if all recited elements remain present. The design-around must remove or fundamentally alter at least one required claim element to defeat a literal infringement finding.
- Watch for lexicography and disavowal. Before relying on the ordinary meaning of a claim term, review the specification for any explicit definition and the prosecution history for any statement that could constitute a clear disavowal of scope. Either can shift the construction in ways that alter the infringement analysis.