The voices of some psychotic patients may sound much louder than what the rest of us hear, and sometimes they may seem to be external to them, but we all hear internal voices. In even earlier times, hearing an internal voice was thought to be a message from God, the devil, or some other external entity. Even today some people who commit crimes say that they were ordered to do it by a voice that they heard. "The devil made me do it."

Hearing internal voices is a natural part of being able to understand and produce language. With the exception of a few people with damage to the language area of the brain, we all have internal voices, and usually they provide very useful information and direction. These voices may orient us to tasks that we need to accomplish, alert us to some kind of danger, review the events of the day, etc. "There's an important meeting tomorrow morning." "Let's get out of here before the trouble starts." "I got quite a lot done this week."

Sometimes inner voices offer us useful advice. "Look both ways before crossing a street," is a voice that most parents deliberately try to instill in their small children in order to protect them from being run over. At other times, an internal voice may simply offer information that is needed to solve a problem, or direct our attention to get back to an unfinished task. "I wonder if those towels are in the laundry." "I'd better get going on that homework if I'm going to get enough sleep tonight."

Infants begin to learn language by listening to parents and other people around them. The first step in this learning process is to remember the sounds that they heard, and slowly begin to recognize repetitions of those sounds and patterns of sounds. As they are doing this, they are also learning to produce sounds, first by babbling, and then gradually adjusting that babbling to approximate the sounds of the language that they are exposed to. Initially both the sounds that they hear, and the sounds that they are learning to produce have no meaning. They are just learning to recognize and produce the sounds of their native language.