An International Guide to
Patent Case Management for Judges

12.5.5 Infringement by equivalence

In following the approach described above, it is important to prevent infringement from going unpenalized through a subterfuge: that of introducing irrelevant variations in a product or process to avoid the appearance that patent claims have been duplicated.⁶³ It is therefore important to bear in mind what was mentioned earlier about the interpretation and scope of claims. Infringement by equivalence is where an opposing party avoids identically reproducing every element of a patent claim by replacing one of its characterizing elements with another that is clearly equivalent. Spanish legislation makes it explicitly clear that patents also protect inventions where apparent discrepancies in an element are found in reality to be equivalent.⁶⁴ Such equivalence means that infringement has in fact occurred, carrying the same legal consequences as literal infringement.

When the comparison of elements is performed as described earlier, attention must be paid to whether a variation in an element that initially appears not to reproduce an element in a patent claim is not in reality a substantial variation from the perspective of a person skilled in the art. It is infringement – not literally but by equivalence (although the legal effect is the same) – if a function, the way it is performed, and the results obtained in solving a problem targeted by a patented claim are essentially replicated. Hence the crucial importance of patent descriptions. The proviso in all of this is that it must be obvious to the skilled person that the variation observed in the element concerned falls within the patent’s scope of protection, based on its claims as interpreted in the overall context of the patent, including its accompanying description and drawings.

As a general rule, an element must be considered equivalent to an element of a claim if in its context it performs the same function to produce the same results from the perspective of a person skilled in the art. However, some additional factors must be considered in reaching that judgment. These include whether the skilled person – from the perspective of the priority date (if earlier, so as to avoid ex post facto judgments) – would have considered the element as falling outside the patent’s scope of protection based on its description, drawings and claims. Consideration must also be given to whether the element would correspond to the prior art or be obvious from the perspective of the prior art. And yet another point to consider is whether the patent owner expressly and unequivocally excluded the element from the claim during the application process to avoid an objection from the examiner based on the prior art.

An approach frequently used to determine this issue of equivalence is the so-called triple identity test, which consists of analyzing whether the element performs the same function, uses the same modus operandi and produces the same result. While particularly useful for mechanical patents, this method may prove inadequate for other types of patents (for chemicals, medicines, etc.) which must be assessed based on a concrete case and an objective application of the rules described above – and from the perspective of a person skilled in the art. It is especially important in this context not to confuse this hypothetical “person” with an expert trial witness, the former being a legal concept and a function of the technical sector concerned, such that the point of reference must be determined according to the particularities of the case.

Another method used in assessing equivalence or non-equivalence comes from British case law (the “Catnic” and “Improver” cases) and is now also used in Spanish forensic practice. It consists of asking and answering up to three questions in sequential order until the situation is clarified. First, does the variant used by the defendant substantially alter the functioning of the invention described in the plaintiff’s patent? If it does, there is no equivalence. If it does not, the process continues with the second question: would the proposed alternative have appeared obvious to the skilled person reading the patent at the time of its publication? If it entails inventive step, there is no equivalence. If it would have appeared obvious, the third question is asked: in the opinion of the skilled person, having read the text of the claims and the patent description, did the patent owner intend to adhere strictly to the terms of the claim, as essential to the invention?

In any case – and this cannot be stressed too often – it is indispensable to methodically analyze, through element-by-element comparison between the patent and the good or service at issue, whether infringement by equivalence has been committed. To be rigorous, it is not acceptable to settle for general considerations about the overall invention. It is necessary to determine precisely what specific element is being substituted by equivalence for an element specified in the patent claim.

On the other hand, an element cannot be considered equivalent if the patent owner made the corresponding element in the patent claim subject to a disclaimer or limitation during the application process.