9.5. Taking account of doubts

An appellant (opponent) is not required to prove that carrying out the invention is inherently impossible; it need only adduce understandable arguments casting doubt on whether the invention can be carried out over the whole scope of the conferred protection on the basis of the patent specification and, if necessary, common general knowledge (T 809/13).

The board in T 1299/15 observed that it was established case law that the opponent (here: appellant) bore the burden of proving an alleged lack of enablement. However, since the patent specification did not describe any embodiment, the appellant in this case could not take such an embodiment as a basis for proving the lack of enablement; instead, it could only invoke a lack of plausibility in support of its case. Having done precisely that, it had shifted the burden of proving the contrary to the patent proprietor (respondent) and, that being the case, the board ultimately decided that the doubts had to go that party's detriment. (See also T 805/17 on the burden of proof and means of evidence in a case where a patent contained so little information that it was considered insufficient even in combination with the skilled person's common general knowledge – dental reconstruction – doubts about availability of a method of manufacturing a blank with the claimed properties).

In ex parte case T 2249/16 the board applied the principle that doubts need not be proven by way of experiments but must at least be substantiated in a technically plausible manner. It observed that the contested decision did not set out any reasons or arguments as to why the skilled person would be unable to carry out the invention.