Contract law differentiates sealed instruments from simple contracts as to undisclosed principals

Evidence

We find no authority for the proposition that a contract under seal may be turned into the simple contract of a person not in any way appearing on its face to be a party to or interested in it, on proof dehors the instrument that the nominal party was acting as the agent of another, and especially in the absence of any proof that the alleged principal has received any benefit from it, or has in any way ratified it, and we do not feel at liberty to extend the doctrine applied to simple contracts executed by an agent for an unnamed principal so as to embrace this case. — Henry M. Hart, Jr. and Albert M. Sacks, The Legal Process, 2510