It was stated in Chapter V of Part I that empirical knowledge of the voice, based on the singer's sensations, is used to supplement and interpret the doctrines of mechanical vocal guidance. This is in the main true, so far as the vocal teacher is aware. But here again the result of the sub-conscious character of empirical knowledge of the voice is seen. As a matter of fact the real situation is the direct reverse of that described in the chapter mentioned. The mechanical doctrines are used in the attempt to interpret the empirical knowledge. This fact is well brought out in the following passage from Kofler: "The teacher must imitate the wrong muscle-action and tone of his pupil as an illustration of the negative side." (_The Art of Breathing_, N. Y., 1889.) Kofler does not touch on the question, how the teacher is able to locate the wrong muscle-action of the pupil. He takes this ability for granted; it is so purely an intuitive process that he does not stop to inquire into the source of this information of the pupil's vocal action. Through his sense of hearing he sub-consciously locates the faults in the pupil's tone-production. His only conscious application of this knowledge is the attempt to explain to the pupil the wrong muscle-action. This he naturally tries to do in the terms of mechanical action and muscular operation. Thus the mechanical doctrine is used in the attempt to explain the empirical knowledge. Yet the teacher is conscious only of citing the mechanical rule, and believes this to cover the entire instruction. In the preceding chapter it was seen that the perfectly produced vocal tone may be considered in a variety of aspects. Each one of these aspects is characterized by a fairly distinct set of sympathetic sensations. Of faulty modes of throat action, as revealed by sympathetic sensations, there is an almost infinite variety. Of this wide variety of forms of throat tension the most prominent are those indicated by sets of sympathetic sensations, the direct opposites of those characterizing the perfect vocal action. Thus the open throat is indicated by one set of sympathetic sensations, the lack of this characteristic of tone by an opposite set, etc. Whatever distinct fault of production the pupil's tone indicates, the master immediately notes the character of the faulty throat action. The master feels, simply and directly, what is wrong with the student's tone-production. Whence this knowledge comes he does not stop to inquire. Suppose the pupil to sing an exercise, and to produce tones which stick in the throat, instead of coming out freely. The master simply hears that the pupil's voice is caught in the throat; he does not observe that he is informed of this condition by muscular as well as auditory sensations.