Materially Affects the Way the Invention Works

Date Published

If it is evident from a reading of the specification, either explicitly or implicitly, that a particular feature materially affects the way the invention works, the feature is essential.

In Catnic Components v Hill & Smith Ltd (1982) RPC 183 at 243 it was stated:

“The question in each case is: whether persons with practical knowledge … would understand … a particular descriptive word or phrase appearing in a claim was intended by the patentee to be an essential requirement of the invention ...

The question, of course, does not arise where the variant would in fact have a material effect upon the way the invention worked.”

Thus, a feature can only be considered non-essential if it does not materially affect the way the invention works.

Conversely, examiners should note that unless it is readily apparent that a feature would not materially affect the way the invention works, then the feature must be considered to be essential. In Ryan v Lum (1989) 14 IPR 513, which concerned a method of cleaning silver involving a sheet of aluminium with a regular pattern of holes, the court observed:

"Neither in the specification nor anywhere else is it claimed that it is the holes themselves which are important in the process. Indeed, the fact that the specification is so general about the number and types of holes that are needed negates to my mind the view that the holes are of great significance to this invention."

See also Rodi and Wienenberger AG v Henry Showell Ltd (1969) RPC 367.

If there is no working interrelationship, nor potential working interrelationship, between the feature and the other features of the claim, it will usually be the case that the feature does not materially affect the way the invention works, i.e. it cannot be an essential feature of the invention, unless it is clear from the specification that the feature is intended to be essential (see Introduction).