It is true in nature, in both organic and inorganic matter, that sound reports the quality of substance, that is, the quality of the sound indicates the quality of the object which produces it. This is very apparent in the animal kingdom. The naturalist knows by the tone of the bird's voice what kind of bird it is. The hunter knows by the voice of a wild animal heard in the distance whether it is carniverous or herbiverous; for in the voice of the former he hears something which is savage, something which tears, while in the latter he hears the softer tones of the milder animal. In this treatise I shall consider the human voice as the natural reporter of the individual, his character, and his physical and mental states. I am not considering the individual in any narrow sense, but in the sense of his entire being-body and mind.
Charles Wesley Emerson's book The Evolution of Expression was a central text in the Monroe Conservatory of Oratory's curriculum in the early twentieth century. It was Emerson's firm belief that communication skills were the key to fulfilling one's potential and that a student who completed this academic program would have success regardless of their chosen endeavor or profession.