Rule 705 Disclosing the Facts or Data Underlying an Expert’s Opinion

When an expert witness testifies in court, they usually don't have to walk through all the background facts and data before sharing their opinion. They can simply state their opinion and explain their reasoning, unless a judge decides otherwise for a specific case.

However, this doesn't mean the other side is left in the dark. During cross-examination, the opposing lawyer can question the expert and make them reveal the facts and data behind their opinion. This gives both sides a fair chance: the expert can testify efficiently, but their reasoning can still be challenged and tested in front of the judge or jury.

This rule helps speed up trials by not forcing every expert to give a long lecture on their methods before getting to the point. At the same time, it protects the other side's right to dig into that reasoning and question whether the expert's opinion actually holds up.