There is no constitutionally or statutorily required form of oath. Federal Rule of Evidence 603 requires only that a witness 'declare that the witness will testify truthfully, by oath or affirmation administered in a form calculated to awaken the witness' conscience and impress the witness' mind with the duty to do so.' The advisory committee notes to Rule 603 explain that 'the rule is designed to afford the flexibility required in dealing with religious adults, atheists, conscientious objectors, mental defectives, and children. Affirmation is simply a solemn undertaking to tell the truth; no special verbal formula is required.' This rule represents no break with the common law, which recognized that the oath's efficacy may depend upon both the general name and nature of the witness' faith and the formula of words or ceremonies which he considers as binding, i.e., as subjecting him to the risk of punishment. But it cannot matter what tenets of theological belief or what ecclesiastical organization he adheres to, provided the above essentials are fulfilled, and it cannot matter what words or ceremonies are used in imposing the oath, provided he recognizes them as binding by his belief. 6 Wigmore, Evidence § 1818 (Chadbourne ...