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A compound question is one that actually asks several things which might require different answers. In a trial, a compound question will likely raise an objection, as the witness may be unable to provide a clear answer to the inquiry. For example, if the attorney cross-examining the witness were to ask, "isn't it true that you murdered your neighbor, then went home and baked a pie which you donated to the Girl Scouts bake sale?", the question could not be answered with a simple "yes" or "no" if only parts of it were true - if, for example, the witness had murdered his neighbor and donated the pie, but had not baked the pie (or had baked it before the murder).
Compound questions are a common feature in loaded questions such as "Have you stopped beating your wife?" The argument is phrased as a single question requiring a single answer, but actually involves two or more issues that cannot necessarily be accurately answered with a single response. By combining the questions "Are you currently beating your wife?" and "Have you ever beaten your wife?", one can make it impossible for someone who has never beaten his wife to effectively answer the question, as phrased.