Speech may be divided into conception, or formulation, and production, or phonation and articulation, of speech (see voice). Speech development in children starts with associating sounds with persons and objects, comprehension usually predating vocalization by some months. Nouns are developed first, often with one or two syllables only; later acquisition of verbs, adjectives, etc., allows the construction of phrases and sentences. A phase of babbling speech, where the child toys with sounds resembling speech, is probably essential for development. Reading is closely related to speech development, involving the association of auditory and visual symbols.

Speech involves many aspects of brain development (hearing, vision, etc.) but three areas particularly concerned with aspects of speech are located in the dominant hemisphere of right-handed persons and in either hemisphere of left-handed persons. Disease of these parts of the brain leads to characteristic forms of dysphasia or aphasia, alexia, etc. Developmental dyslexia is a childhood defect of visual pattern recognition. Stammering or stuttering, with repetition and hesitation over certain syllables, is a common disorder in some cases representing frustrated left-handedness. Dysarthria is disordered voice production is due to disease of neuromuscular control of voice. In speech therapy attempts are made to overcome or circumvent speech difficulties, this being particularly important in children (see also deafness).