Under what condition can a terminal disclaimer be filed?

A terminal disclaimer can only be filed when both patents are owned by the same entity. This is because a terminal disclaimer is a mechanism that allows a patent owner to overcome certain patentability issues, such as double patenting, by agreeing that the term of the second patent will not extend beyond that of the first patent. Therefore, the two patents must be linked in terms of ownership to ensure that the same entity is bound by the disclaimer's terms.

When both patents are owned by the same entity, the patent owner can effectively prevent the second patent from providing a patent term that overlaps or extends beyond the first, which mitigates the concern of unjustly extending exclusivity derived from separately filed applications for the same invention. This is crucial for maintaining the balance of rights and prevents the potential for one entity to monopolize aspects of an invention in a way that could harm innovation or competition.

In scenarios where patents are owned by different entities, or when the patents are for different inventions or do not share conflicting claims, a terminal disclaimer would not be appropriate or effective, thus those scenarios would not allow the filing of a terminal disclaimer.