These ideas have to be understood in Dhyana, or meditation. We hear a sound. First, there is the external vibration; second, the nerve motion that carries it to the mind; third, the reaction from the mind, along with which flashes the knowledge of the object which was the external cause of these different changes from the ethereal vibrations to the mental reactions. These three are called in Yoga, Shabda (sound), Artha (meaning), and Jnâna (knowledge). In the language of physics and physiology they are called the ethereal vibration, the motion in the nerve and brain, and the mental reaction. Now these, though distinct processes, have become mixed up in such a fashion as to become quite indistinct. In fact, we cannot now perceive any of these, we only perceive their combined effect, what we call the external object. Every act of perception includes these three, and there is no reason why we should not be able to distinguish them.