Music is the art and science of combining vocal or instrumental sounds or tones in varying melody, harmony, rhythm and timbre, especially so as to form structurally complete and emotionally expressive compositions. To appreciate music the listener need not know the definition of music. The knowledge of science is desirable in that it helps him or her to substantiate his or her conclusions. However, it is not a must, because music and human psyche are so inter-related that the mind involuntarily responds to music like a plant to sunlight.