This chapter describes the major goals and types of explanation, with examples of research from our laboratory, to claim that the approaches can be mutually complementary. It explains animal behavior considering the meaning of explanation. Hempel's treatment of the term fits the activities of practicing scientists. The chapter describes the approaches used in experiments from my laboratory that have employed pharmacological manipulations. It focuses on the alternative explanations that were given for the observed input-output regularities. Although Maricq, Roberts, and the author concluded that the results suggest that methamphetamine increases the speed of an internal clock used by rats in time discrimination tasks, the three experiments described in this report could have been interpreted with a behavioristic input-output analysis. In the report, it appeared that methamphetamine was selected solely on the basis of previous empirical work that showed that it affected performance of rats on timing tasks.