The principles elaborated in the preceding chapters permit us to describe and analyze a large fraction of the learned behavior of people and other animals. But were we to terminate our account of behavior with the phenomena of operant conditioning, classical conditioning, stimulus control, and aversive contingencies, we would still be forced to admit that the bulk of complex human behavior had either been left untouched or at best dealt with rather indirectly. The activities that might be classified as complex human behaviors are, of course, extremely diverse, and in this chapter we will examine concept acquisition and modeling, and then turn to verbal behavior itself which seems so intimately associated with many forms of complex human behavior.