The basis for the empiricist approach to sound perception is the necessity of experience and prior knowledge. We receive a great variety of sound stimuli. However, we select, register, and identify readily those sounds of which we have prior knowledge. The faster and more accurately we answer the empirical question "What is it?" the closer we come to identifying the form or the nature of the sound stimulus. For example, by asking what the form of the sound is, empiricists seek to distinguish random noise from purposeful sound. The sound of a church bell is perceived as an organized and purposeful sound exerted by an identifiable source and it has a particular purpose.