5.5.3.3 Purposive Construction

Date Published

Key Legislation: 

Patents Act:

  • s7 Novelty, inventive step and innovative step  
  • s7A Meaning of useful  
  • s18 Patentable inventions
  • s40 Specifications 
  • s41 Specifications: micro-organisms  

Purposive approach

A patent specification should be given a purposive construction rather than a purely literal one.

The "purposive" approach requires that allowance be made for inherent difficulties in, or unforeseen implications of, drafting, which have resulted in the literal construction not being the one the drafter has obviously intended. The underlying rationale for this approach is a fair exchange to inventors for the contribution made by their inventions.​​​​​​​

In Catnic Components Limited v Hill and Smith Limited (1981) FSR 60 the court stated:

"… The question in each case is: whether persons with practical knowledge and experience of the kind of work in which the invention was intended to be used, would understand that strict compliance with a particular descriptive word or phrase appearing in a claim was intended by the patentee to be an essential requirement of the invention so that any variant would fall outside the monopoly claimed, even though it could have no material effect upon the way the invention worked.

The question, of course, does not arise where the variant would in fact have a material effect upon the way the invention worked. Nor does it arise unless at the date of publication of the specification it would be obvious to the informed reader that this was so. Where it is not obvious, in the light of then-existing knowledge, the reader is entitled to assume that the patentee thought at the time of the specification that he had good reason for limiting his monopoly so strictly and had intended to do so, even though subsequent work by him or others in the field of the invention might show the limitation to have been unnecessary. It is to be answered in the negative only when it would be apparent to any reader skilled in the art that a particular descriptive word or phrase used in a claim cannot have been intended by a patentee, who was also skilled in the art, to exclude minor variants which, to the knowledge of both him and the readers to whom the patent was addressed, could have no material effect upon the way in which the invention worked.