Patents of Addition: What is Their True Status?

Following is the comment I received to one of my earlier posts titled “A PCT Application for a Patent of Addition”:

“Can you please answer if i have priority date in India for my parent invention which is published in patent gazette and i have few days left for completion of 12 months duration from priority date for filing PCT application. Now i wish to file patent of addition before Indian patent office but i want to file single PCT application for both the said application. How shall i proceed? Is it possible to file a club application claiming both the priorities? if yes, how shall be the description and claims? (like the claims of patent of addition should be in continuation of claims of parent invention”

I felt it would be best to clarify the status of patents of addition in order to comprehensively answer the question.

Patents of addition, in my opinion, are also amendments effected to the complete specification. The only difference being that they are “positive amendments” by way of additions to the description and claims, as opposed to being disclaimers, deletions or clarifications. This means what is sought to be filed as a patent of addition too must have the same or cognate inventive step as the originally filed/granted patent application/patent as the case may be.

As reflected by Section 54(1) of the Patents Act, a patent of addition may be filed during the pendency of the parent patent application or after its grant, unlike a CIP in the US which must be filed during the pendency of the non-provisional (complete) specification.

Section 55 of the Act makes it clear that the term of the patent of addition ends along with the parent patent. This is an exception to Section 53 which states that the term of a patent is 20 years from the date of filing of the application.

However, what is the position of law with respect to the priority date of claims claimed in the patent of addition? The common flaw is to assume that since the term of the patent of addition ends along with the parent patent, it has the same priority date as that of the parent patent. I do not think the approach behind this assumption is valid.

For the purposes of understanding priority, Section 11 must be looked into which states that each claim of a complete specification shall have a priority date. I had written in an earlier post that priority dates are decided on the basis of “fair disclosure”. Similarly, in a patent of addition, if the claim is fairly based on the matter disclosed in the complete specification of the parent patent application, then it would have the same priority date as that of the complete specification of the parent patent.

However, if the claim is fairly based on matter disclosed in the application for patent of addition, its priority date shall be the filing date of the patent of addition.

If this be the case, what are rules of establishing anticipation for a patent of addition? If a document discloses material which is identical to the new embodiment claimed in the patent of addition which has the filing date of the patent of addition as its priority date, and the document was published after the publication of the parent patent but before the filing date of the patent of addition, then such a document may be validly used as anticipatory prior art against the patent of addition.

It must be understood that Section 56 of the Patents Act bars only the use of the complete specification of the parent patent to allege lack of inventive step in the patent of addition, however there is no bar on using the complete specification of the parent patent or any other published document to establish lack of novelty in the patent of addition. 


That said, it must also be understood that sometimes the patentee or the applicant may have disclosed an embodiment in the written description of the parent patent, but may not have claimed it. In such situations, the written description of the parent patent may not be used to allege lack of novelty of the patent of addition which claims the embodiment because that would defeat the very purpose of filing the patent of addition.

Now, to address the comment of the anonymous commentator, it is certainly possible to file a single PCT application clubbing matter disclosed in the parent patent and patent of addition provided the PCT application is filed within 12 months from the date of priority of the parent patent. However, the PCT application must refer to both the parent patent and patent of addition, and must therefore refer to two priority dates if the claims in the patent of addition are based partly on the parent patent and the patent of addition.

Comments and corrections are welcome!