What is the difference between positive reinforcement and negative reinforcement?

Positive reinforcement strengthens a behavior by adding a desirable stimulus after the behavior occurs. For example, giving a child praise or candy for completing homework increases the likelihood of doing homework again. Negative reinforcement strengthens a behavior by removing an aversive stimulus after the behavior occurs. For example, taking an aspirin removes a headache, making you more likely to take aspirin in the future. Both reinforcement types increase the target behavior. The key distinction is adding something pleasant versus removing something unpleasant.