In many cases, an invention develops gradually. After an initial patent application is filed, additional components, improvements or alternatives are added, and a further application or a PCT application is subsequently filed. In such circumstances, subject to the applicable legal requirements, the later application may rely on multiple priority claims, a mechanism commonly referred to as Multiple Priorities.
This mechanism offers a significant advantage. It may allow an earlier date to be preserved for subject matter already disclosed in the first application, while a later date may apply to new subject matter introduced in a subsequent application.
However, multiple priorities in a patent application also create legal complexity. Not every element of the invention, and not every part of a claim, is necessarily entitled to the same effective date. Therefore, where an application relies on several earlier applications, it is necessary to examine separately which subject matter is supported by each application and determine the relevant effective date for each part of the invention.
The risk is particularly significant where a PCT application is filed more than 12 months after the first application, but within 12 months of a second application. In such a case, entitlement to the claimed priority must be examined separately for each element and each claim.
For a general explanation of the patent filing process and its various stages, see The Steps for Registering a Patent.
How Does the Multiple Priorities Mechanism Work?
Assume that a first application, Priority A, is filed on January 1, 2025. A second application, Priority B, is filed on November 1, 2025, incorporating the subject matter of the first application together with new subject matter. A PCT application is then filed on February 1, 2026.
In this situation, subject matter properly disclosed in Application A may be entitled to the January 1, 2025 date, provided that the priority claim based on A is valid. Subject matter first disclosed in Application B may be entitled to the November 1, 2025 date. New subject matter first introduced in the PCT application will generally receive the PCT filing date.
This result is not automatic. For each element, it is necessary to determine whether the priority application relied upon actually discloses that element to the required standard and whether the other conditions for recognizing the priority claim are satisfied.
As a result, several different effective dates may exist within the same patent family.
Advantages of Multiple Priorities
The principal advantage of multiple priorities is the ability to preserve an earlier date for different parts of an invention.
An applicant may file an initial patent application quickly, continue developing the invention during the priority year, and subsequently file another application containing improvements, alternatives or additional components.
This can be particularly important where technological development continues after the first filing and the applicant does not wish to lose the earlier date for subject matter that has already been disclosed.
Multiple priorities may also provide greater flexibility in claim drafting. This is particularly significant before the EPO, where the partial priority doctrine may, in appropriate circumstances, recognize different effective dates for different parts of the scope of a single claim.
The Principal Risk: The First Priority Claim May Not Be Valid
The fact that a PCT application lists several priority applications does not establish that each priority claim is valid.
Where the PCT application is filed more than 12 months after Priority A, it is necessary to determine whether A can still serve as a valid basis for priority and, in particular, whether restoration of the right of priority may be available.
If the priority claim based on A is not recognized, subject matter first disclosed in A may not benefit from its earlier filing date.
By contrast, subject matter first disclosed in Priority B may benefit from the date of B, provided that the later application was filed within the applicable period and the other requirements for recognition of priority are satisfied.
Accordingly, when analyzing a patent application based on several earlier applications, it is not sufficient to review the list of priority applications appearing on the application. The effective date of each material element should be determined separately.
PCT and Restoration of the Right of Priority
Under the PCT, restoration of the right of priority may, in appropriate circumstances, be requested where the international application was filed after the expiry of the 12-month priority period but within the additional period permitted under the PCT Rules.
The applicable examination may be based on the due care criterion or the unintentionality criterion, depending on the Receiving Office and the standard it applies.
Under the due care standard, the question is whether the applicant took the reasonable measures required in the circumstances to meet the filing deadline. This involves a factual examination of the reasons for the delay and the steps taken in relation to the particular filing.
Accordingly, where a PCT application is filed after expiry of the 12-month period, it should be determined promptly whether restoration may be requested and what facts and evidence are required to support the request.
For further information about the PCT procedure and national phase entry in Israel, see PCT National Phase Entry in Israel.
Israel: The Due Care Standard
In Israel, priority rights are governed, among other things, by the Israeli Patents Law and the rules applicable to PCT applications entering the Israeli national phase.
Where a PCT application was filed after expiry of the 12-month period but within the period in which restoration may be requested, restoration of the priority right may be available in appropriate circumstances.
Israel applies the due care standard. Accordingly, the applicant must demonstrate that reasonable measures were taken to ensure that the international application was filed on time.
The practical consequence is that a favorable restoration decision during the PCT phase does not necessarily conclude the priority analysis. It is necessary to consider how the priority right will be examined in Israel and what effective date will apply to the relevant subject matter in the Israeli proceedings.
For a broader overview of examination in Israel, see Patent Prosecution in Israel.
United States: Effective Filing Date
In the United States, the central question is the effective filing date of the claimed invention.
Where a case is based on several priority applications, each claim, and in some cases each material element of a claim, should be examined to determine the earliest date to which it is entitled for the claimed subject matter.
If particular subject matter is not properly supported in an earlier application, it will not benefit from the earlier date with respect to that subject matter.
In practice, an effective-date analysis should therefore be conducted for the claims and their material elements. The effective filing date is important, among other things, in determining which publications or applications may qualify as prior art.
Accordingly, where several priority applications exist, merely listing them in the PCT application is insufficient. The legal and factual basis for entitlement of each part of the claim to the earlier date should be examined.
EPO: Multiple Priorities and Partial Priority
The EPO permits multiple priority claims and may recognize more than one priority in relation to a single claim.
Under the partial priority doctrine, a broad claim may contain one part that is entitled to an earlier priority date and another part that is not.
For example, if a claim includes alternatives A and B, where A was disclosed in one priority application and B was disclosed in another, each alternative may, in appropriate circumstances, be attributed its respective effective date.
However, multiple priorities do not permit a new combination to be created artificially from different priority documents. If feature C is disclosed in one document and feature D in another, but the combination C+D is not properly disclosed in any relevant priority application, the combination does not automatically receive the earlier date.
The practical question is therefore what specific subject matter is disclosed in each priority document and what part of the claim scope is supported by that disclosure.
Self-Collision and Toxic Priority Before the EPO
Priority entitlement may be particularly important where several applications exist within the same patent family.
If part of a claim is not entitled to the asserted priority date, an earlier or parallel application may, in appropriate circumstances, become relevant as prior art.
The partial priority doctrine may, where applicable, allow a broad claim to be treated conceptually as containing different parts with different effective dates.
This may be especially significant in situations commonly referred to as self-collision or toxic priority, where an application from the same patent family may affect the patentability of a later application.
Accordingly, where several priority documents exist, it is important to examine not only whether a formal priority claim was made, but also what subject matter is actually supported by each priority document.
How Should a Priority Audit Be Conducted?
Where a patent application is based on multiple priorities, it is advisable to prepare a Priority Map identifying the first application in which each element, alternative and combination in the claims was disclosed.
The analysis should determine whether the first priority claim is valid, what subject matter is supported by the first application, what additional subject matter is supported by the second application, and the earliest disclosure date of each element.
It is also necessary to examine whether publications occurred between the priority dates, whether particular subject matter was disclosed to the public during the intervening period, and what effective date applies to that subject matter in each jurisdiction in which protection is sought.
Where the PCT application was filed after expiry of the 12-month period, it should also be determined whether restoration is or was available and what effect the restoration decision may have in the jurisdictions in which national phase entry is intended.
Particular attention should be given to potential exposure to self-collision, internal prior art arising from the patent family itself, and external publications occurring between the relevant filing dates.
Where new subject matter was introduced in the later application, the analysis should also consider support in the original disclosure and the effect of the new material on priority entitlement and the scope of protection.
Does a PCT Restoration Decision Bind the National Offices?
Not necessarily.
Three separate questions should be distinguished: whether the PCT application was validly filed, whether the priority claim is valid, and whether national phase entry was completed on time.
A positive answer to the first or third question does not necessarily guarantee a positive answer to the priority question.
A Receiving Office under the PCT may accept a restoration request under the criterion applicable before it, while a national office may examine priority entitlement under the law and standards applicable in that jurisdiction.
In Israel, for example, the issue is examined under the due care standard. Therefore, even where restoration was accepted during the PCT phase, its effect on the Israeli proceedings should be considered separately.
Can Multiple Priorities Be Claimed in a PCT Application?
Yes. A later application may claim multiple priorities, provided that each priority claim satisfies the relevant requirements and the subject matter for which priority is claimed is supported by the corresponding application.
Merely identifying several priority applications does not determine the effective date of all claims. Substantive entitlement to each claimed priority date must be examined.
What Happens If a PCT Application Is Filed More Than 12 Months After the First Application?
If the application was filed within the period during which restoration may be requested, it may be possible to restore the priority right.
The applicable criterion, the circumstances of the delay and the evidence required to support the request should be examined.
In addition, it is necessary to consider separately how a restoration decision obtained during the international phase will be treated in the national jurisdictions in which the applicant enters the national phase.
Do All Claims in an Application Receive the Same Priority Date?
Not necessarily.
Where an application contains subject matter disclosed at different times, different parts of the claims may be entitled to different effective dates.
Accordingly, where an application relies on several priority documents, each claim and the subject matter on which it is based should be analyzed separately.
What Is Partial Priority Before the EPO?
Partial priority may, in appropriate circumstances, recognize that part of the subject matter contained within a broad claim is entitled to an earlier priority date, while the remaining part is entitled to a later date.
This mechanism is particularly important where a claim includes alternatives or elements that were disclosed at different stages during development of the invention.
Practical Conclusion
Where multiple priority claims exist, it is not sufficient to rely on the list of priority documents appearing in the patent application.
Each element and each claim should be analyzed separately to determine the relevant effective date in Israel, the United States, before the EPO and in other important jurisdictions.
This is particularly important where the PCT application was filed more than 12 months after the first priority application, where technological features were added during the priority year, or where information was published between the relevant filing dates.
A structured Priority Audit can identify publications that may become prior art, assess the need for restoration, and enable the claim strategy to be adapted to each jurisdiction.
In complex cases involving multiple priorities, the analysis should preferably be conducted before filing the PCT application or before entering the national phases, together with a patent attorney familiar with the structure of the patent family and the international filing strategy.
For further details, see my book: Y. Drori, “Patent Law,” Praelstein Ginosar Publishing (2023), Vol. I, pp. 579–580.
