Rule 618 Impeachment of expert by learned treatises

Here's what this rule means when an expert witness testifies in court.

If someone is an expert witness (like a doctor or scientist), lawyers can challenge their opinions using published books, articles, or other written materials on the subject. But first, the material has to be shown to be trustworthy and respected in that field. This can be proven three ways: the expert admits it's a reliable source, another expert says it's reliable, or the judge officially recognizes it as reliable.

Once that's established, a lawyer can use these written materials during cross-examination to point out that the expert's testimony doesn't match what respected sources in their field say. This can hurt the expert's credibility if their opinion contradicts well-known, trusted publications. An expert can also bring up these materials themselves during their own testimony if they relied on them to form their opinion.

There's an important limit here. These treatises and articles can only be used to question the expert's credibility. They cannot be used as direct proof of facts in the case. In other words, the jury can consider the material when deciding whether to believe the expert, but they can't treat statements from the book or article as evidence that proves what actually happened.