John b. watson and b. f. skinner were the principal contributors to the behavioral perspective.

Believed that psychology should ONLY study what can be observed and measured and that behavior can be molded by the environment we live in.

Believed "No such thing as free will".
 
 Both John B. Watson and BF Skinner were main contributors in the world of psychology in a behavioral approach. John B. Watson was the one who created the school of behaviorism. He studied behaviors and made a lot research on human and animal behavior and advertising. BF Skinner, on the other hand, was the one who started reinforcements and conditioning. He believed that behaviors are highly influenced by the consequences of the act.