Logic mechanisms operate to define the position of at least one mechanical output based on the position of two or more mechanical inputs, and employ at least one control element that functions to determine (at least in part) whether an output is moved, and which provides the same function in more than one position. Some mechanisms are configured to determine, based on the input positions, whether a path to transmit motion to an output exists or does not exist. Some mechanisms are configured to determine, based on the input positions, whether or not motion of a driven element can be accommodated without moving an output.