A professor is not one who knows, but one who professes to know, and thus is constantly in the position of inviting challenge.... He professes publicly where everyone is invited to come and challenge, and at any time he must be willing and able to defend it openly against all comers. The degree is originally a chivalric devicea gauntlet of defiance to all rivalsand not a safe rampart or dug-out for a scholar to hide behind in safe immunity from any challenge.