Evidence

A collateral matter is one that would not reasonably call into question the accuracy of the witness's testimony if it is not true.

Non-collateral contradiction is when extrinsic evidence calls into question the truth of a statement, such as by bias.

If extrinsic evidence does not reasonably call into question the accuracy of a witness's testimony, it is collateral evidence and not admissible under FRE 403.

• Because the court does not want a bunch of mini-trials over little, barely-related matters which would just waste time.
• You can still ask the question of whether that is true or not though.
• This is similar to subsequent remedial measures.

It is possible for one to have previously remembered something, but not know it now without lying. They could have forgotten. Forgetfulness is not an inconsistent statement unless it is faked.

Evidence of a prior inconsistent statement can be read in court. FRE 613.

A prior inconsistent statement can be admitted even if it is not direct impeachment. (Barrett v. United States allowed one to testify he heard the witness testify something else earlier.)