Provisional Priority – How Secure Is It?

A provisional application is a technical document filed at a patent office to establish a filing date as early as possible. It typically lacks the legal style and structure of a patent application. Provisional applications are commonly associated with the United States Patent Office, but technical reports or scientific papers can with minor modification also meet the minimum criteria for fixing a first filing date at other patent offices. A full patent application prepared by a patent attorney later requests priority from the provisional. 

Many discussions about provisional applications focus on the danger of filing too little. Inventors rush to secure a filing date, submit a sketchy presentation, and later discover that more material should have been included. But a recent EPO Board of Appeal decision, T 1235/24, shows that the uncertainties associated with provisional priority are not necessarily avoided even if you file a lot of material in your provisional application.  

Priority claims at the European Patent Office

In EPO case law, a patent claim is only entitled to priority if all the features it specifies are either expressly disclosed or directly and unambiguously implied in the priority document. If a claim contains at least one feature which is not entitled to priority, the claim is treated as having been filed on the filing date of the EPO application (rather than the date of the priority application). In other words, an unsupported feature can move the effective filing date of the claim forward by a year. 

This is not necessarily a problem we always must avoid. There is no harm in a claim which lacks priority when no relevant prior art exists. But in T 1235/24 document D1 became available to the public between the filing date of the provisional priority application and the filing date of the later European application. This brought entitlement to priority, i.e. the validity of the priority request for the claim at hand, to the forefront. The EPO considered D1 to be normal prior art because the claim contained features which could not be found in the provisional US application, and thus the claim was not entitled to priority. The applicant filed an unsuccessful appeal against this refusal of priority, arguing that the claimed features had been presented already in the provisional. 

Why priority was denied?

The priority document in T 1235/24 was not a hastily prepared invention report. The document ran to almost one hundred pages and contained detailed descriptions of a Unified Speech and Audio Coding (USAC) reference model. It included decoder architectures, bitstream syntax definitions, mathematical formulas, tables, algorithm descriptions and extensive pseudocode.  

The contested patent claim concerned context-based decoding of audio data. Large parts of the priority document were indeed devoted to that topic, but it did not describe the operating principle in more abstract terms. In the Board of Appeal’s opinion (point 12)  

“(…) the features of the claim have each been isolated from the context in which they were disclosed (in the priority document), generalized, and combined with other features, equally isolated from their respective contexts and generalized.” 

This statement resembles the familiar intermediate generalization objection which the EPO can present against claim amendments. If features A, B and C can each be found somewhere in the application text, but in different contexts, a generalizing claim amendment specifying A+B+C is not allowable unless the text clearly indicates that these features can be combined. In other words, the text should contain the generalizations which are claimed.  

In T 1235/24, lack of generalization and legal terminology in the provisional application led the Board of Appeal to conclude that the claimed invention had not been presented in the provisional. Separate statements and definitions in the provisional could be linked to the claimed features, but that was not enough to entitle the claim to priority.  

Practical takeaways

There’s nothing wrong with filing a software design document, scientific paper or engineering report as a provisional application, but it should be remembered that such documents are written for information sharing and practical implementation, not for legal certainty. T 1235/24 reminds us that even a highly sophisticated and comprehensive provisional application can fall short if it keeps legally important generalizations hidden.  

When we use provisional filings to set an early filing date, we should not disregard the risk that (a) strong prior art may become public before a real patent application is filed and (b) the priority may later be considered invalid.  

Both (a) and (b) depend on future events that are unknown to us when the provisional is filed. Nevertheless, we can reduce the risk (1) by including some legal generalizations in our provisional application and/or (2) by filing a real patent application as soon as possible. If we deliberately wait until the very end of the priority year before filing a real patent application, we should be confident that future priority requests will be valid. A more urgent filing schedule may be justified if we are doubtful.