Some psychologists, experimental and otherwise, felt so strongly about aversive control that they raised their children as much as possible by positive reinforcement alone. Negative reinforcement, escape from an aversive stimulus, is very common and necessary in the natural human environment because aversive stimuli occur so widely and frequently. The reinforcement is arbitrary because there is no reinforcer currently maintaining the desired behavior or behavior similar to it in the child's repertoire. Such arbitrary social reinforcement differs in two ways from the natural reinforcer that was just described. First, the performance that is reinforced is specified narrowly rather than broadly as the large class of behaviors that can get rid of the natural aversive stimulus. A second property of arbitrary reinforcement is that the individual's current repertoire does not influence the behavior it produces nearly as much as is the case with natural reinforcers.