A fundamental requirement of the teacher’s art lies in the correcting of mental concepts, and in the overcoming of inhibitions so that the interfering muscular contractions may be eliminated and the mental concept may become similar to that of the singer who is born with a ‘great natural voice.’ The first law for the teacher of voice will have to be that no direction may be given the pupil which pertains to the direct control of any narrow group of muscles taking part in the act of phonation. All directions to the pupil must either be of a general nature, or must pertain to groups of muscles which are not or should not be used in the act of phonation. Thus, any direction to the pupil which pertains to the position of the larynx, the base of the tongue, the palate and so forth, or to the control of the breath is physiologically impossible of accomplishment DURING THE ACT OF PHONATION. The result of such directions is further confusion of the mental concept, which is extremely harmful technically, and a sense of helplessness which inevitably results from an attempt to accomplish the impossible.
Stanley, Douglas. “The science of voice.” Journal of the Franklin Institute 211.4 (1931): 405-455.