Although it is possible to amend a patent application after filing, it is important that any amendment does not add subject matter that was not in the application as filed.
An intermediate generalisation is a form of added subject matter objection that is often raised at the European Patent Office. Such an objection is effectively arguing that an amendment adds subject matter because the amendment isolates a feature that was originally only disclosed in combination with other features. For example, if a patent application refers to a “read-only memory”, an Examiner may raise an intermediate generalisation objection if the application is amended to simply refer to a “memory” without mentioning that this memory is read-only. This is because the feature of a memory was originally only disclosed in combination with the idea that the memory is read-only. Thus, the Examiner is arguing that the more general idea of any form of memory is not disclosed in the application as filed, and hence is added subject matter.
It can be possible to argue against an intermediate generalisation objection if (a) the relevant feature is not related or “inextricably linked” to the other features it is disclosed alongside; and (b) the application as a whole justifies isolation of the feature. For example, if a new car engine is disclosed in combination with the fact that the engine is placed in a saloon car, it may be possible to argue against specifying a saloon car on the grounds that the type of car is unrelated to the new engine. However, the European Patent Office are relatively strict in this regard, so even in examples like this, it can be hard to convince a European Examiner to allow any amendments that do not specify the saloon car, unless the application explicitly states the car could also be another type of car (e.g. a hatchback).
Given the European Patent Office are very strict on added subject matter and intermediate generalisations, it is important to take this into account when drafting a patent application. In particular, when drafting, it is important to emphasise which features are optional. Also, where separable features are described in combination, it is sensible to emphasise that these features can additionally be used in isolation from one other.