Claims Interpretation and Construction
Purposive construction
Claims are construed purposively, not literally: the court asks what the skilled addressee would understand the patentee to have meant, reading the claim in the context of the whole specification. Candidates must know that the description can illuminate but cannot rewrite a clear claim, and that the claim defines the monopoly boundary.
The skilled addressee and common general knowledge
The notional skilled person is competent in the field but unimaginative, and possesses the common general knowledge of the art at the priority date. Traps: using an expert's idiosyncratic reading; using post-priority knowledge; treating dictionary definitions as controlling over the specification's own definition.
Essential integers and variants
Where a claim lists integers, ask whether each is essential to the working of the invention. A variant that takes the substance of the invention but substitutes a non-essential integer may still infringe. Conversely, an integer the patentee insisted was essential cannot be read out to catch a variant.
Worked example
A claim to a container "formed of plastics material" with a lid "sealed by heat welding". If the specification teaches that the weld is what achieves the seal, the integer is essential; a container sealed by adhesive falls outside. If the specification teaches that any fluid-tight seal works, the weld is non-essential and the adhesive version may infringe. Rule of thumb: the specification's stated purpose of each integer determines whether it is essential.