In this paper we present two design guidelines, causal order and continuity, to be used as rules of thumb for designing intuitive interactions based on principles of causal reasoning. We propose that designing interactions to behave like real-world systems of cause and effect makes them more intuitive. Using these basic principles avoids the limitations inherent to specific metaphors. In three experiments, participants solved puzzles using variations of a novel graphical interface. Participants using interfaces that were consistent with the causal guidelines consistently solved the puzzle faster than participants using inconsistent interfaces. We also discuss common interactions already consistent with the causal guidelines as well as areas where the guidelines are likely to apply successfully. The causal order guidelines provide specific utility while also demonstrating how principles of causal psychology can be applied to help interface designers better convey the functionality of their interfaces.