An experimental result is shown to have generality when it is observed in different environments, organisms, and so on. For example, the principle of reinforcement generalises over species, settings, responses, and reinforcers. In a pigeon, the peck-for-food relationship depends on deprivation for food in the immediate past. For humans, who have an extensive capacity for operant conditioning, going to a soda machine to get a cold drink is an effective contingency on a hot afternoon. In both examples, reinforcement is the operating principle.