In Commonwealth v. Corbett, the defendant was charged with sexually assaulting a five-year-old child. As in most cases of sexual abuse, the child was the only witness to the abuse, and the prosecution viewed her testimony as essential. However, before the prosecutor could present the child's testimony to the jury, it was necessary to qualify her for the oath. Most courts require that child witnesses have some understanding of the difference between the truth and lies and the importance of telling the truth, 2 and Massachusetts is no exception. A child who fails the qualifying questions is considered testimonially incompetent, and is not allowed to testify.