A description of collective degree of freedom as a dynamical variable

As a sequel to the elementary consideration of the properties of the redundant ignorable variable, we extend the argument to the Schrödinger field. The Bohm-Pines theory of the collective mode will be worked out systematically from this point of view. It will be observed that the variable representing the collective mode is introduced in connection with the symmetry of the system, unlike the way in which Bohm and Pines assumed the variable in a rather ad hoc manner.