602 Lack of personal knowledge

If someone testifies in court, they have to actually know what they're talking about firsthand. They can't guess, repeat rumors, or share something they only heard secondhand. Before a witness can testify about something, there has to be enough proof that they really saw it, heard it, or experienced it themselves.

The proof of personal knowledge can come from the witness's own statements, but it doesn't have to. Other evidence can also show that the witness was in a position to know what they're testifying about. For example, another witness or a document might confirm that the first witness was actually there and saw what happened.

This rule works a bit differently for expert witnesses, like doctors or engineers who give opinions based on their training. Under a separate rule, experts are allowed to base their opinions on information they didn't personally witness, such as reports, tests, or facts given to them by others. So this personal knowledge requirement mainly applies to regular witnesses testifying about ordinary facts, not experts giving professional opinions.