common knowledge exception

In professional liability claims, expert testimony is often needed to assist the jury in assessing whether the defendant's professional performance or conduct conformed to the standard of care for that professional and the particular activity involved. The expert opines on whether the professional was in breach of that duty and whether that was the proximate cause of the claimed damages. The common knowledge exception is a rule that allows a layperson, not an expert, to testify as to whether the defendant's professional standard of care was breached, dispensing with the need for expert testimony. This exception is limited and may not apply in all cases or states.