Short answer. An answer-in-intervention. That pleading is for an intervenor who unites with the defending party in resisting the plaintiff's claim; a complaint-in-intervention, by contrast, is used when the intervenor is instead asserting his or her own independent claim against one or all of the original parties.
What the law says
The intervenor shall file a complaint-in-intervention if he or she asserts a claim against either or all of the original parties, or an answer-in-intervention if he or she unites with the defending party in resisting a claim against the latter.
Rule 19, Section 3 — Pleadings. Read the full provision →
Two pleadings, two different roles
An intervenor entering into a pending case is not limited to just one single form of pleading regardless of what that intervenor actually wants to accomplish by intervening. The rule instead provides two genuinely distinct options — a complaint-in-intervention or an answer-in-intervention — with each one suited to a meaningfully different posture the intervenor may want to take within the existing case. That structural choice mirrors the same claimant-versus-defender roles the original parties already occupy, letting an intervenor slot into whichever side of that divide actually matches what they are trying to accomplish.
When a complaint-in-intervention is the right pleading
A complaint-in-intervention is the pleading to be filed if the intervenor is actually asserting a claim of their own against either or all of the original parties already in the case. This particular pleading is the appropriate vehicle to use when the intervenor is not simply supporting an existing side of the dispute, but is instead bringing an entirely affirmative claim of the intervenor's own into the ongoing litigation.
When an answer-in-intervention is the right pleading
An answer-in-intervention, by clear contrast, is filed if the intervenor instead unites with the defending party in resisting a claim already being made against that latter party. This particular pleading fits an intervenor whose real interest is purely defensive in nature — aligning with the party already defending against the plaintiff's claim, rather than pressing forward any independent claim of the intervenor's own.
Why picking the right one matters
Because these two pleadings serve genuinely different functions — one asserting an affirmative claim, the other simply supporting an existing defense — filing the wrong one could seriously mischaracterize what the intervenor is actually trying to accomplish by intervening in the case at all. An intervenor who only wants to help the defendant resist the plaintiff's claim, without raising any independent claim of their own, should therefore use the answer-in-intervention rather than the complaint-in-intervention. Filing a complaint-in-intervention when only an answer-in-intervention was warranted could also expose the intervenor to affirmative defenses or counterclaims that a purely defensive pleading would not invite, so more is at stake in the choice than mere labeling.
Related provisions
- Rule 19, Section 3 — Pleadings
- Rule 19, Section 2 — Time to intervene
- Rule 19, Section 4 — Answer to complaint