Researchers have been concerned with internal and external validity for decades, and the discussion continues. The present proposal is that there are less important and more important senses in which one can interpret internal and external validity, and these can be integrated with a taxonomy that includes theoretical, auxiliary, statistical, and inferential assumptions. The integration sheds light on recent exchanges in the literature on validity and suggests that the vaunted internal-external validity trade-off is false for more important senses of internal and external validity; internal and external validity increase or decrease together when there is an emphasis on underlying theories. Finally, the integration implies the desirability of some changes in typical research advice and practice.
Keywords: empirical hypotheses; external validity; inferential hypotheses; internal validity; statistical hypotheses; theories.