ABA is an applied science devoted to developing procedures that will produce observable changes in behavior. It uses principles developed by such research, in particular operant conditioning and classical conditioning. Behavior analysis adopts the viewpoint of radical behaviorism, treating thoughts, emotions, and other covert activity as behavior that is subject to the same rules as overt responses. This represents a shift away from methodological behaviorism, which restricts behavior-change procedures to behaviors that are overt, and is the conceptual underpinning of behavior modification.