An ambiguity in the claims may lead to an insufficiency objection. However, ambiguity also relates to the scope of the claims, i.e. Art. 6 (see GL/PCT‑EPO F‑IV, 4). Normally, therefore, an ambiguity in a claim will lead to an objection under Art. 5 only if the whole scope of the claim is affected, in the sense that it is impossible to carry out at all the invention defined therein. Otherwise an objection under Art. 6 is appropriate.[GL/ISPE 4.12; 5.58; ]

In particular, where a claim contains an ill-defined ("unclear", "ambiguous") parameter (see also GL/PCT‑EPO F‑IV, 4.11) and where, as a consequence, the skilled person would not know whether they were working within or outside of the scope of the claim, this, by itself, is not a reason to deny sufficiency of disclosure as required by Art. 5. Nor is such a lack of clear definition necessarily a matter for objection under Art. 6 only. What is decisive for establishing insufficiency within the meaning of Art. 5 is whether the parameter, in the specific case, is so ill-defined that the skilled person is not able, on the basis of the disclosure as a whole and using common general knowledge, to identify (without undue burden) the technical measures necessary to solve the problem underlying the application at issue.

There is a delicate balance between Art. 5 and Art. 6 which has to be assessed on the merits of each individual case.