Under what condition can a claim be joined by a plaintiff against an adverse party?

Joining claims in civil procedure allows a plaintiff to consolidate multiple claims against an adverse party in a single lawsuit. For this to happen, subject matter jurisdiction over each claim is essential. This means that the court must have the authority to hear the type of claim being presented, which typically ties into whether the claims arise under federal or state law and if they meet the requirements for diversity or federal question jurisdiction.

Subject matter jurisdiction ensures that the court is capable of resolving the issues presented in the claims. If a court lacks jurisdiction over any of the claims, it cannot adjudicate the relevant matters, making subject matter jurisdiction the primary requirement for joining claims.

The other options do not accurately reflect the necessary conditions for joining claims. A shared interest in the claim or unrelated claims may have relevance in certain contexts, but they do not establish the foundational requirement of subject matter jurisdiction. Similarly, requiring all defendants to agree to the joining of claims is not a prerequisite for claim joinder under civil procedure rules. The only absolute necessity is that the court must have subject matter jurisdiction over each claim for them to be joined and heard together effectively.