Medicine and law share common antecedents as the first and second professional classes. Because of their ancient roots they share many doctrines unique to professional practice. The "judgment rule," "continuous representation," fairly short statutes of limitation and deference to experts in determining the standard of practice are each applicable to both.

Less well known is the common and unique New York rule for deposing a professional as an expert concerning the standard of care and the witnesses' own conduct. This widely unknown rule is that a defendant physician or lawyer may be called and questioned both as to his factual knowledge of the case and as an expert for the purposes of establishing the generally accepted standard of professional practice. This is true whether the defendant is noticed as an expert or not.