Before developing language, infants establish certain pre-linguistic faculties. Their auditory system learns to discern differences in tone and volume. An infant of six months can already detect emotion from intonation. Based on the sound of a person's voice, he will know whether that person is sad, happy, or even afraid. Infants also develop the ability to differentiate between human-produced sounds and non human-produced sounds.
Between the ages of six months to one year, young people begin to attach meaning to the sounds they hear. The language centers in the brain double during this rapid developmental stage, enabling the little one to grasp the basic words, including commands, nouns, subjects, and verbs. Typically, young people at this stage still depend quite heavily on nonverbal cues in their communication.
Most people begin to understand sentence structure around 2 years old. They begin constructing complete sentences and engaging in meaningful conversation. In this stage, young people start conforming their language to grammatical rules that govern structure and meaning. They also start to enunciate more clearly. It's important to encourage verbal communication at this stage; practice helps to ensure proper language development.
Between ages 4 and 8, people acquire the ability to use language abstractly. They can understand concepts like fairness, good, and evil. They understand how to use mental projection in order to imagine or predict the future. This stage stretches several years, but teaching children to read early and engaging in conversation with them can help accelerate their language development.