This monograph is not statistical in the sense of developing specific statistical tools. It looks instead at pre-statistical assumptions about dependent variables and the causal order governing them.Professor Davis spells out the logical principles that underlie our ideas of causality and explains how a practical researcher can discover causal direction, irrespective of the statistical technique used. He stresses that knowledge of the "real world" is important and repeatedly challenges the myth that causal problems can be solved by statistical calculations alone.He shows researchers how to think through the unstated reasons that lead them to choose their variable order and introduces the notion of a causal system. This system of indirect effects, causally spurious effects, and signed effects provides a rich and exact tool for discussing the fascinating and complex subject of causation.