Under what condition may a party use an expert witness if they failed to disclose required material?

The use of an expert witness after a party has failed to disclose required material can hinge on the concept of whether the failure to disclose was harmless. If the omission does not affect the fairness of the proceeding or the ability of the opposing party to prepare for trial, the court may find that the failure to disclose was harmless and allow the expert witness to be utilized.

In civil procedure, the rules surrounding expert witness disclosure are designed to ensure that both parties have a fair opportunity to address the evidence that will be presented. If the failure to disclose is deemed harmless, the court is often inclined to permit the testimony, thereby prioritizing the resolution of cases on their merits rather than on procedural missteps.

The other conditions, such as having a valid reason, requiring court approval, or needing mutual agreement from both parties, do not address the threshold issue of whether the nondisclosure has a significant impact on the case. These other options involve more subjective measures that do not directly relate to the established standard concerning harmless error in procedural contexts.