2.4.9 Doctrine of Mechanical Equivalents

Date Published

In General Tire & Rubber Co v The Firestone Tyre & Rubber Co Ltd (1972) RPC 457 at page 485 it was stated:

"To determine whether a patentee's claim has been anticipated by an earlier publication it is necessary to compare the earlier publication with the patentee's claim ...

The construction of these documents is a function of the court, being a matter of law, but, since documents of this nature are almost certain to contain technical material, the court must, by evidence, be put into the position of a person of a kind to whom the document is addressed ...."

In the course of dealing with an objection to the grant of a patent on the grounds of lack of novelty, the courts have had regard to the doctrine of mechanical equivalents, i.e. whether, on the evidence before the court, the difference between the claimed invention and the alleged anticipation represents no more than the substitution of an inessential feature with an obvious equivalent.

See R D Werner & Co Inc v Bailey Aluminium Products Pty Ltd (1989) 13 IPR 513.

It should be noted that the courts appear to have taken the view that if a feature of the claim has a mechanical (i.e. functional) equivalent in the alleged anticipation, then ipso facto the feature must be inessential. Furthermore, the existence of mechanical equivalents has been determined from evidentiary material (which in general is not available to examiners), and not as a matter of construction.

However, during examination, the issue to determine is whether a prior art document contains a clear description of, or clear instructions to make, something that possesses all the essential features of a claim. For this reason, examiners should not concern themselves whether an inessential feature of a claim replaces a feature of the prior art with a mechanical equivalent.