Like many othe rbehaviorists, Hull believed that most behavior could be expained by previous conditioning. However, Hull developed a hypothesis and then a theory, called drive reduction theory, that states that biological deprivation creates needs and may supercede or 'rewrite' early conditioning. These needs activate drives that motivate new behavior. This behavior is goal-directed. Other psychologists would argue that not all motivating stimuli, however, had to be tied in to the survival needs of an organism.
