Why are speech disorders not classified only by how they sound to a listener?

Classifying speech disorders solely by how they sound to a listener is considered unsatisfactory because such labels are subjective and describe only the final, audible result rather than the underlying cause.1

Relying on perceptual impressions is analogous to early medicine, which often classified diseases based on visible or audible symptoms rather than their true origins. Just as early theories incorrectly attributed malaria to "bad air" before the discovery of blood parasites, symptomatic labels for speech—such as stuttering or lisping—fail to identify the physiological or psychological basis of the condition.1

Modern speech pathology aims to group disorders by their underlying origins, whether they are organic (involving structural lesions or metabolic disturbances) or functional (involving habits, breathing, or emotional factors). Because organic structure and living function are deeply interconnected, a comprehensive diagnosis must look beyond surface-level symptoms to understand the total picture of the disturbance, including how a patient adapts to or learns to overcome their specific limitations.12