A patent claim is the part of a patent that actually matters legally.
The description explains the invention. The claims define what the owner can stop other people doing, and infringement and validity are both decided against them.
Each claim is one sentence with three parts, and the structure is identical across every technology.
Once you can see the three parts, claims stop being unreadable.
(This covers claims in patents. A mining claim under US mineral law is an unrelated concept sharing the word.)
The three parts
1. A fluid separator comprising: a housing defining a flow path; a baffle disposed within the flow path, the baffle defining an aperture; and a biasing element coupled to the baffle.
| Part | In the example |
|---|---|
| Preamble | "A fluid separator" |
| Transition | "comprising" |
| Body | Everything after — the elements |
One sentence, always. The semicolons separate elements; they do not end sentences.
The transition word decides the most
| Transition | Meaning |
|---|---|
| Comprising | Open — extra elements do not avoid the claim |
| Consisting of | Closed — nothing beyond what is recited |
| Consisting essentially of | Additions allowed if they do not materially affect it |
| Including, containing | Generally treated as open |
| Having | Depends on context |
Almost every claim uses "comprising", which is why the most common non-infringement argument fails.
"Our product has additional features" is not a defence. A product containing everything recited plus more still infringes an open claim.
"Consisting of" is rare and narrow, appearing mainly in chemical compositions where excluding additional ingredients is the point.
The preamble
| Situation | Limiting? |
|---|---|
| Merely states a purpose or intended use | Usually not |
| Gives life and meaning to the claim | Yes |
| Provides antecedent basis for body terms | Yes |
| Recites structure relied on for patentability | Yes |
This is contested regularly. A preamble saying "A method for treating wastewater" may or may not limit the claim to wastewater, and the answer depends on how the rest of the claim and the prosecution history read.
Check for antecedent basis. If the body says "the flow path" and only the preamble introduced it, the preamble is doing structural work.
The body
| Feature | Detail |
|---|---|
| Elements separated by semicolons | Each is a requirement |
| "the" versus "a" | "the" refers back; "a" introduces |
| Relationships between elements | Frequently limiting |
| Functional language | "configured to", "adapted to" |
| Every element must be present | For infringement |
Antecedent basis matters when reading. "A baffle" introduces it; "the baffle" refers to the one already introduced. A "the" with no antecedent is a §112 defect.
Relationships are elements too. "Coupled to", "disposed within", "upstream of" — each is a requirement that has to be satisfied.
Independent and dependent
| Independent | Dependent | |
|---|---|---|
| Refers to another claim | No | Yes |
| Scope | Broadest in its chain | Narrower |
| Contains | All its own elements | The parent's elements plus more |
| If the parent is invalid | — | May still survive |
| If a product avoids it | — | Avoids everything depending on it |
2. The separator of claim 1, wherein the biasing element comprises a helical spring.
Claim 2 includes everything in claim 1 plus the spring. It is narrower, not different.
Read the independent claims first. Falling outside all of them ends the analysis, because every dependent claim requires its parent's elements.
Claim types
| Type | Reaches |
|---|---|
| Apparatus / device | Makers, sellers, importers, users |
| Method / process | Whoever performs the steps |
| System | Combinations, sometimes across parties |
| Composition of matter | The substance itself |
| Product-by-process | The product, defined by how it is made |
| Means-plus-function | Only disclosed structures and equivalents |
Method claims raise the divided infringement question. Where steps are split between a service and its customer, no single party performs them all, and attribution requires direction or control.
Means-plus-function claims are narrower than they read. Under §112(f) they are limited to structures disclosed in the specification, so "means for biasing" covers the spring you described and its equivalents, not every possible biasing mechanism.
Reading a claim against a product
| Step | Action |
|---|---|
| 1 | Split into elements, one per limitation |
| 2 | Note the transition word |
| 3 | Test each element separately |
| 4 | Check relationships between elements |
| 5 | Every element present? |
| 6 | If one is absent, consider equivalents — then estoppel |
Split at every limitation, not every clause. "Biased toward the inlet by a spring" contains two requirements.
Overall similarity is not the test. It produces errors in both directions — concluding infringement because products look alike, or non-infringement because the accused product has extra features.
Worked example: element by element
Claim 1 from above, against a competitor product.
| # | Element | Product | Present? |
|---|---|---|---|
| 1 | A housing defining a flow path | Cast aluminium body | Yes |
| 2 | A baffle disposed within the flow path | Internal plate | Yes |
| 3 | The baffle defining an aperture | Central opening | Yes |
| 4 | A biasing element | Magnetic assembly | Yes |
| 5 | Coupled to the baffle | Direct coupling | Yes |
| Result | Infringes |
The product also has a filter, a heater, and a digital display. None of that helps, because the transition is "comprising".
Now claim 2
| # | Element | Product | Present? |
|---|---|---|---|
| 1–5 | As claim 1 | — | Yes |
| 6 | Biasing element is a helical spring | Magnetic | No |
| Result | Does not infringe claim 2 |
Infringing claim 1 and not claim 2 is normal. Dependent claims are narrower, and a product can fall inside the broad claim while avoiding the narrow one.
Which is why finding one infringed claim is enough. Infringement of any single claim is infringement. See patent claim chart.
What claims cannot do
| Limitation | Consequence |
|---|---|
| Cannot be broadened after filing | Beyond what the description supports |
| New matter cannot be added | Alternatives not described are unavailable |
| Amendments surrender scope | Permanently, via estoppel |
| Cannot cover ineligible subject matter | Abstract ideas, natural laws |
| Must be definite | §112 requires clear boundaries |
The description sets the ceiling. Claims can be narrowed during prosecution and broadened only within what was already disclosed.
Every amendment to overcome prior art is permanent. It bars equivalents in the surrendered range. See prosecution history estoppel.
Construction comes before comparison
| Source | Weight |
|---|---|
| The claims themselves | Highest, including claim differentiation |
| The specification | Very high |
| The prosecution history | High |
| Extrinsic evidence | Lowest |
Decide what the words mean before comparing anything. A mapping done without construing the disputed terms changes the moment a court reads them.
Claim differentiation is a useful tool. If claim 2 adds "wherein the spring is helical", claim 1's "biasing element" is presumably broader than a helical spring. See claim construction.
Claim count and fees
| Included | Beyond | |
|---|---|---|
| Total claims | 20 | Excess fee each |
| Independent claims | 3 | Excess fee each |
| Multiple dependent claims | 0 | Substantial surcharge |
Twenty and three is why most patents look the way they do. The structure follows the fee schedule.
Before reading claims at all
| Check | Why |
|---|---|
| Is the patent in force? | 58.6% are abandoned before term |
| Who owns it now? | The front page is out of date |
| Which claims survived any challenge? | Narrowed claims read differently |
| Ipiry Patent Survival Curve v1.0 | Rate |
|---|---|
| Survive the 3.5-year fee (2022 cohort) | 85.8% |
| Survive the 7.5-year fee (2018 cohort) | 64.6% |
| Reach full term (2014 cohort) | 41.4% |
Computed from 27,273,654 USPTO maintenance fee records covering 8,262,336 US utility patents — see the patent survival curve.
Three minutes in Patent Center can end the exercise before any claim is read.
Patent claim: the checklist
- Find the three parts — preamble, transition, body.
- Read the transition word first. "Comprising" means extra features never help.
- Check whether the preamble limits, particularly for antecedent basis.
- Split the body into elements, one per limitation.
- Read every independent claim before any dependent one.
- Treat relationships between elements as requirements.
- Test each element separately. Never overall similarity.
- Watch for means-plus-function language — it is narrower than it reads.
- Construe disputed terms before comparing anything against them.
- Check the patent is in force first. Most are not.