Hypothetical questions can help facilitate conversations on judgments about the perceived likelihood or potential consequences of an event or an action. They can also help reveal hidden or flawed assumptions. Supreme Court justices, for instance, often use hypothetical questions to test the outer boundaries of what the advocate is asking the court to declare and of what the court may have to decide. Such questions are also permissible in trials and depositions. Lawyers often use hypothetical questions to help frame facts for the jury. This column aims to clarify the circumstances under which hypothetical questions are permissible for both lay and expert witnesses.

One such misconception is the common belief that a lay witness may never answer a hypothetical question. Indeed, courts have stated, in dicta, that "the ability to answer hypothetical questions is 'the essential difference' between expert and lay witnesses." See United States v. Henderson, 409 F.3d 1293 (11th Cir. 2005) (quoting Teen–Ed v. Kimball International, 620 F.2d 399 (3d Cir.1980)). Under the federal rule of evidence, witnesses may only testify to opinions or inferences "which are rationally based on the perception of the witness, and helpful to a clear understanding of the witness' testimony or the determination of a fact in issue, and not based on scientific, technical, or other specialized knowledge within the scope of Rule 702." The rule does not forbid a lay witness to answer a hypothetical question, however; it only requires that their testimony be based on personal perceptions or observations and that any part of a witness's testimony that is based upon scientific, technical, or other specialized knowledge within the scope of Rule 702 be governed by the standards of Rule 702 and the corresponding disclosure requirements.