Major theorists in behaviorism include John B. Watson, Ivan Pavlov, Edward Thorndike, B.F. Skinner, and Clark Hull. Behaviorism is based on the idea that all behaviors are acquired through conditioning, and can be studied systematically through interaction with the environment without consideration of internal mental states. The two major types of conditioning are classical conditioning, involving learned associations between stimuli, and operant conditioning, where behaviors are associated with consequences like rewards and punishments.