In Part IV the information about the vocal action obtained from the two sources is combined,--the scientific knowledge of mechanical processes, and the empirical knowledge derived from attentive listening to voices. Throat stiffness is then seen to be the one influence which can interfere with the instinctively correct action of the voice. The most important cause of throat stiffness is found in the attempt consciously to manage the mechanical operations of the voice. In place of the erroneous principles of mechanical instruction, imitation is seen to be the rational foundation of a method of Voice Culture. The mystery surrounding the old Italian method is dispelled so soon as the possibility is recognized of teaching singing by imitation. Practical rules are outlined for imparting and acquiring the correct use of the voice, through the guidance of the sense of hearing. The singer's education is considered in its broadest sense, and training in tone-production is assigned to its proper place in the complex scheme of Voice Culture. During the past twenty years the author has found opportunity to hear most of the famous singers who have visited America, as well as a host of artists of somewhat lesser fame. In his early student days the conviction grew that the voice cannot reach its fullest development when mechanically used. Siegfried does not forge his sword, and at the same time think of his diaphragm or soft palate. Lucia cannot attend to the movements of her arytenoid cartilages while pouring out the trills and runs of her Mad Scene. A study of the theoretical works on Vocal Science, dealing always with mechanical action and never with tone, served only to strengthen this conviction. Finally the laws of physiological psychology were found to confirm this early belief. Every obtainable work on Voice Culture has been included in the author's reading. No desire must be understood to make a display of the results of this study. One citation from a recognized authority, or in some cases two or three, is held sufficient to verify each statement regarding the accepted doctrines of Vocal Science. As for the practical features of modern methods, the facts alleged cannot in every case be substantiated by references to published works. It is, however, believed that the reader's acquaintance with the subject will bear out the author's statements.