Two distinct lines of approach were laid down for studying the operations of the voice. First, the manner of investigation usually accepted as scientific. This is, to study the vocal mechanism; to determine, as far as possible, the laws of its operation, in accordance with the principles of anatomy, acoustics, mechanics, and psychology. Second, the manner of investigation generally called empirical. This begins with the observing of the tones of the voice, considered simply as sounds. From the tones we work back to the vocal organs and apply to them the information obtained by attentive listening. Both of these means of investigation have been utilized; we are now in possession of the most salient facts obtainable regarding the vocal action. Separately considered, neither the scientific nor the empirical study of the voice is alone sufficient to inform us of the exact nature of the correct vocal action. The next step is therefore to combine the information obtained from the two sources, scientific analysis and empirical observation. Let us begin by summing up all the facts so far ascertained. Tone-production in singing is a conscious and voluntary muscular operation. The vocal organs consist of a number of sets of voluntary muscles, of the bones and cartilages to which these muscles are attached, and of the nerves and nerve centers governing their actions. The precise nature of the muscular contractions of tone-production, whether correct or incorrect, is not known. These contractions occur in accordance with established laws of acoustics and mechanics. Under normal conditions the vocal organs instinctively respond to the demands of the singer, through the guidance of the sense of hearing. The ability of the vocal organs to adjust themselves properly may be upset by some influence apparently outside the singer's voluntary control. Study of the vocal mechanism does not inform us of the meaning of the correct vocal action, nor of the difference between this action and any other mode of operation of the voice.