Introduction

Harmless Error on Appeal

Introduction

Federal Rule of Criminal Procedure 52(a) is a single sentence: "Any error, defect, irregularity, or variance that does not affect substantial rights must be disregarded."¹ Two features of that text carry most of its weight. The first is the verb "must," which makes the command mandatory, so a reviewing court has no discretion to reverse over a mistake that falls within the rule.² The second is the phrase "substantial rights." The four labels before it (error, defect, irregularity, and variance) are broad enough to reach nearly any departure from correct procedure, which leaves the substantial-rights screen to do the sorting.³ Rule 52 as a whole pairs this command with a separate provision for errors that were never raised at trial, a contrast that closes this chapter.⁴

Harmless-error review is the last filter an appeal passes through. By the time a court reaches it, the appellant has already preserved the objection by objecting or making an offer of proof at trial, and the court has already found that the trial judge actually erred.⁵ Proof of a mistake still does not end the inquiry, because reversal is not automatic. The reviewing court must separate errors serious enough to require a new trial from those that are not, and the dividing line is whether the error affected the outcome.⁶ The intuition behind that line is easy to grasp, since few trials reach the end without some slip, and the people applying slippery or discretionary rules in an adversary system will sometimes err. Setting aside every conviction that contains a mistake would send cases back for retrial over errors that changed nothing, and the same principle appears in the civil rules and in the statute governing appellate review generally.⁷ The intuition also carries a hazard. A rule that waved through every small-looking error could wave through one that quietly decided a close case, so the inquiry looks to the effect of the mistake on the result, which a minor-looking error can sometimes have.

This chapter takes the rule in stages. It first explains why the rule exists and what "substantial rights" means for ordinary errors, then turns to constitutional errors, which must satisfy a stricter test before a court may call them harmless. Next come the circumstances in the record that make an error harmless, the rule's reach into grand jury proceedings, and the contrast with plain error, which governs mistakes that were never preserved. The place to begin is the question the rule itself raises: why would a legal system instruct its judges to ignore mistakes that have been proven?