David C. Taylor, The Psychology of Singing
“ The ear is trained by exercise in its own function,—hearing. The more attentively we listen to music the higher do we develop our ability to discriminate between musical sounds. Moreover, natural endowments vary in different individuals, with regard to the ear, as with all other human faculties. To appreciate fully the wonderful insight into vocal operations conveyed by the sympathetic sensations of tone, a naturally keen musical ear is required; further, this natural gift of a good ear must be developed by attentive listening to music, vocal and instrumental, carried on through several years. ”
