Under what condition is an amendment to the complaint allowed to relate back to the original complaint?

An amendment to the complaint is allowed to relate back to the original complaint when it is filed within the time allowed for serving the original complaint. This principle is rooted in the need to promote judicial efficiency and fairness by ensuring that amendments do not unfairly disadvantage the opposing party.

The rule regarding relation back typically serves to protect plaintiffs from losing their claims due to minor errors or changes in circumstances that occur before the statute of limitations expires. If the amendment is intended to correct a defect or include a claim that arose out of the same conduct, transaction, or occurrence set forth in the original pleading, and if it is made within the permissible time frame for serving the original complaint, then it can be treated as if it was part of the initial filing.

The other options are not conditions that would allow for relation back. Presenting new evidence, agreeing to new terms, or involving a different cause of action does not address the emphasis on the timing of the filing in relation to the original complaint, which is the primary condition for relation back to apply.