Positive reinforcement involves rewarding an action after it has been performed by an organism. This only is the case when the reward is present.
For example, a dog receiving a treat after fetching a ball. The dog would be less likely to fetch the ball if the treat was not there. Hence, this would decrease the likelihood of the action being repeated.
Negative reinforcement involves strengthening behavior of an organism by removing an outcome which is negative or a stimulus which is aversive.
For example, a person is more likely to put on sunscreen if they have already been burned once. Hence, this will increase the likelihood of the behavior being repeated.
