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

An expert witness can share their opinion in court without first walking through every piece of evidence or data that led to that opinion. They can just state what they think and explain their reasoning in a general way. The judge can change this if needed, but normally the expert doesn't have to prove their homework before giving their conclusion.

The other side still gets a chance to dig into the details. During cross-examination, the lawyer questioning the expert can ask them to explain exactly what facts or data they relied on. This gives the opposing side a chance to test whether the expert's opinion is actually well supported or if it's based on weak or incomplete information.

In short, this rule lets expert testimony move faster by letting the expert lead with their opinion. But it also protects fairness by allowing tough questions later about what that opinion is really based on.