Catnic Components Ltd. v. Hill & Smith Ltd.

Catnic Components Ltd. v. Hill & Smith Ltd. [1982] R.P.C. 183 is a leading House of Lords decision on the nature of a patent and in particular the methods of claim construction.

Catnic Components had a patent for a steel lintel, used to provide structural support over a door or window opening in a brick wall. The lintel is hollow, being made from sheet steel pressed into a rectangular or trapezoidal shape with a wind to anchor the device to the surrounding brickwork. Part of the specification required a bar to "extend vertically". Hill & Smith created a virtually identical invention that had a bar that extended at an upwards slant, only 6 degrees from being completely vertical. Despite the difference the device worked entirely in the same way as Catnic's invention.

Catnic sued for patent infringement. At trial, the judge held there was an infringement under the "pith and marrow" doctrine. The Court of Appeal of England and Wales overturned the ruling as it held that the "vertical" requirement was an exact and essential element of the patent. The Law Lords reversed the decision of the Court of Appeal, finding that there was an infringement, and affirmed the use of purposive construction in patent interpretation.

Lord Diplock held that a patent must be read in a "purposive" manner that focuses on the essential features of the patent. He famously stated:

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