Much behavior is not reinforced every time it is emitted, and the pattern of intermittent reinforcement strongly affects how fast an operant response is learned, what its rate is at any given time, and how long it continues when reinforcement ceases. The simplest rules controlling reinforcement are continuous reinforcement, where every response is reinforced, and extinction, where no response is reinforced. Between these extremes, more complex "schedules of reinforcement" specify the rules that determine how and when a response will be followed by a reinforcer.