Notional claim splitting: an Australian perspective on multiple priorities

Multiple priorities within a single claim are recognised under Article 4F of the Paris Convention, allowing different parts of a patent claim to benefit from distinct priority dates. While Europe has fully recognised multiple priorities within a single claim for many years, other jurisdictions, including Australia, have adopted a more restrictive approach.

Historically, Australia has recognised multiple (and partial) priorities only for simple linguistic alternatives. However, a recent decision by the Australian Patent Office (APO) suggests that functional alternatives may also be recognised. This potential relaxing of the approach to "notional claim splitting" is significant due to the existence of poisonous priority in Australia.

Notional claim splitting in Australia

Notional claim splitting involves treating a single patent claim as if it were multiple separate claims, each assigned a different priority date based on its first disclosure. The statutory basis for this concept is s 43(3) of the Patents Act 1990 (Cth), which provides:

Where a claim defines more than one form of an invention, then, for the purposes of determining the priority date of the claim, it must be treated as if it were a separate claim for each form of the invention that is defined.

Section 43(3) was introduced in 1969 to address an issue first identified in Thornhill’s Application [1962] RPC 199, whereby the UK Patents Act 1949 – upon which the Australian Patents Act 1952 (Cth) was based – did not provide recognition for different priority dates within a single claim.

While EPO Enlarged Board of Appeal clarified in G 1/15 that entitlement to multiple priorities cannot be refused on the basis of form, Australian courts have interpreted s 43(3) relatively narrowly to cover only simple linguistic alternatives.

Federal Court recognises linguistic alternatives

The first clear guidance was provided in AstraZeneca AB v Apotex [2014] FCAFC 99, in which the Full Federal Court considered whether the following claim could be notionally split into different forms corresponding to each possible non-phosphate counter anion.

Priority Kat

A pharmaceutical tablet comprising [rosuvastatin] or a pharmaceutically acceptable salt thereof as the active ingredient and an inorganic salt in which the cation is multivalent, provided that … the counter anion to the inorganic salt is not a phosphate. [emphasis added]

In declining to invoke s 43(3), the Full Court considered that not every variant within the scope of a claim qualifies as a separate form of the invention; the provision applies only when a claim explicitly defines alternatives or distinct forms. In contrast, The Federal Court in Nichia Corporation v Arrow Electronics [2015] FCA 699 notionally split the following claim because it "envisage[s] and provide[s] for different forms of the invention" with respect to the selection of specific elements.

A light emitting device, including a light emitting component and a phosphor … [wherein] said phosphor contains a garnet fluorescent material including at least one element selected from the group consisting of Y, Lu, Sc, La, Gd and Sm, and at least one element selected from the group consisting of Al, Ga and In, ….  [emphasis added]

These decisions support the view that only clearly defined linguistic alternatives justify notional claim splitting in Australia.

APO recognises functional alternatives

A recent APO decision, Brolock Pty Ltd v Fuzhou Autran Industrial Co., Ltd [2025] APO 4, was the first to apply notional claim splitting to functional alternatives. The invention relates to damping hinges for controlled closing of a door or gate having two possible camming surface configurations: a first configuration using complementary inclined surfaces, and a second configuration using a roller bearing on an inclined surface.

Although the claims did not envisage and provide for different linguistic alternatives, the Hearing Officer determined that the claims could be notionally split into two different forms based on functional alternatives: one involving "surface-to-surface contact" (the first configuration) and the other involving "line-to-line contact" (including but not limited to the second configuration). In arriving at these two forms, the Hearing Officer emphasised that the notionally split claims must be non-overlapping in scope and collectively cover the original claim scope.

Poisonous priority

The AstraZeneca decision raised concerns about poisonous priority in Australia, which occurs when parts of a claim have different priority dates. If the claims cannot be notionally split under s 43(3), and the earlier priority document is published before the later priority date, the earlier priority document can become prior art against the entirety of the claim.

Poisonous priority is especially problematic for broad claims covering multiple embodiments, in which case careful claim drafting is essential to avoid self-collision. Where possible, claims should be drafted such that each claim has one priority date by including different forms of the invention in separate claims. If this is not possible, clearly delineating claim features with different priority dates as alternatives can also assist.

Concluding remarks

Although the APO's decision in Brolock is not binding, it signals a potential shift away from a strictly literal interpretation of notional claim splitting. However, until further guidance is provided by courts or legislature on the application of s 43(3), it remains prudent to include claim features with different priority dates in separate claims, or as clearly defined alternatives, when seeking patent protection in Australia.