Case Comment

Catnic Components Ltd. v.
Hill & Smith Ltd.

citation(s): (1982) R.P.C. 183 (H.L. per Lord Diplock)

copyright 1997 Donald M. Cameron, Aird & Berlis





The Catnic patent called for a lintel (the bar that goes across the top of a window to carry the weight of the bricks laid above it) to have a rear member which should "extend vertically".

Hill copied the Catnic design, then after receiving a writ from Catnic, changed the design so that the rear member was inclined 6 or 8 degrees from the vertical. This resulted in the Hill lintels being 0.6 or 1.2 per cent weaker in their load bearing capacities. Functionally, this was a negligible difference.

The Trial Judge, Whitford J., held that there was no literal infringement but there was infringement under the "pith and marrow" doctrine.

The Court of Appeal held that the limitation that the rear member should "extend vertically" was an essential feature and there could be no infringement of the "pith and marrow".

The Decision

At p. 242

"... both parties to this appeal have tended to treat `textual infringement' and infringement of the ‘pith and marrow’ of an invention as if they were separate causes of action, the existence of the former to be determined as a matter of construction only and of the latter upon some broader principle of colourable invasion. There is, in my view, no such dichotomy; there is but a single cause of action and to treat it otherwise, particularly in cases like that which is the subject of the instant appeal, is liable to lead to confusion."

At p. 242-243:

"My Lords, a patent specification is a unilateral statement by the patentee, in words of his own choosing, addressed to those likely to have a practical interest in the subject matter of his invention (i.e. "skilled in the art"), by which he informs them what he claims to be the essential features of the new product or process for which the letters patent grant him a monopoly. It is called "pith and marrow" of the claim. A patent specification should be given a purposive construction rather than a purely literal one derived from applying to it the kind of meticulous verbal analysis in which lawyers are too often tempted by their training to indulge. 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 the 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."

At p. 243:

"...upon analysis of the speeches in this House in Van Der Lely v. Bamfords the difference of opinion between Lord Reid and the remainder of their Lordships appears to have been due to his thinking that it would be obvious to the informed reader that dismounting the (foremost) rather than the (hindmost) wheels was an immaterial variant, whereas the majority were not satisfied that this was even the fact, let alone that this was obviously so. In the bracelet case, Rodi and Wienenberger A.G. v. Henry Showell Ltd. where this House was more evenly divided, the difference between the majority and the minority appears to have turned upon their respective views as to whether the particular variant alleged to be an infringement had a material effect upon what were claimed to be the advantages obtained by the patented invention - as to which they differed.  In the third of the trilogy of leading cases in this House upon this topic, the ampicillin case, Beecham Group Ltd. v. Bristol Laboratories Ltd. [1977] F.S.R. 215, the descriptive phrase was "an amino group in the alpha position". In the alleged infringing antibiotic, hetacillin, this amino group had been temporarily converted by a further chemical reaction into a molecular structure that was no longer an amino group; but the reaction was reversible and upon being put to use as an antibiotic, (which necessitated contact with water) it reverted to its original form as an amino group and in that form produced its prophylactic effects. This House unanimously held that this temporary masking of the amino group amounted to an immaterial variant. It would be obvious to anyone skilled in the specialised art of selecting and synthesising polymers for use as antibiotics that the essential feature of the invention was that when put to use for its intended purpose, the product should have an amino group in the alpha position; and that, accordingly, the patentee's reference to this feature of his claim cannot have been intended by him to exclude products in which the amino group in that position was temporarily displaced during a period before the product was put to any prophylactic use."

At p. 244:

"The essential features of the invention that is the subject of Claim 1 of the patent in suit in the instant appear are much easier to understand than those of any of the three patents to which I have just referred; and this makes the question of its construction simpler. Put in a nutshell the question to be answered is: Would the specification make it obvious to a builder familiar with ordinary building operations that the description of a lintel in the form of a weight-bearing box girder of which the back plate was referred to as "extending vertically" from one of the two horizontal plates to join the other, could not have been intended to exclude lintels in which the back plate although not positioned at precisely 90 degrees to both horizontal plates was close enough to 90 degrees to make no material difference to the way the lintel worked when used in building operations? No plausible reason has been advanced why any rational patentee should want to place so narrow a limitation on his invention. On the contrary, to do so would render his monopoly for practical purposes worthless, since any imitator could avoid it and take all the benefit of the invention by the simple expedient of positioning the back plate a degree or two from the exact vertical.

It may be that when used by a geometer addressing himself to fellow geometers, such expressions descriptive of relative position as "horizontal", "parallel", "vertical" and "vertically" are to be understood as words of precision only; but when used in a description of a manufactured product intended to perform the practical function of a weight-bearing box girder in supporting courses of brickwork over window and door spaces in buildings, it seems to me that the expression "extending vertically" as descriptive of the position of what in use will be the upright member of a trapezoid-shaped box girder, is perfectly capable of meaning positioned near enough to the exact geometrical vertical to enable it in actual use to perform satisfactorily all the functions that it could perform if it were precisely vertical; and having regard to those considerations to which I have just referred that is the sense in which in my opinion "extending vertically" would be understood by a builder familiar with ordinary building operation. Or, putting the same thing in another way, it would be obvious to him that the patentee did not intend to make exact verticality in the positioning of the back plate as essential feature of the invention claimed."

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