B.F. Skinner’s key principle of learning, stating that all animals’ behaviour operates on the environment with consequences that modify the tendency to repeat the behaviour. Rewarding consequences make repeating the behaviour more likely. Skinner called this reinforcement. For instance, if a non-verbal child is rewarded for making a verbal request this should reinforce the occurrence of this behaviour. These ideas are central to the ABA approach to autism intervention. (See also reinforcement and ABA.)