RelationshipsThe relationships rule – any idea or thing can be related to any other idea or thing – is characterized by two elements: action and reaction. Relationships are often unseen. It is therefore critically important to explicate the salient relationships that exist in any system under study. One must also recognize the many types of relationships that exist within systems and the differences among them. When seeking answers to questions or solutions to problems, people frequently look for causal relationships and often mistake correlation for causation. This is a fundamental thinking error that occurs frequently in many types of research. Applying the relationships rule helps us to not only understand complex types of interrelation, such as webs of causality (in addition to more linear causal processes), but also to critically examine relation- ships as important parts of any system one might study.Systems thinkers have long understood the importance of relationships, including complex ones involving feedback. Considering relationships is foundational to cybernetics (Bateson, 1970; Wiener, 1948) and system dynamics (Forrester, 1971; Kambiz et al. 2000), a focus on relationships is a natural outgrowth of analyzing systems because the parts of a whole can be connected (related to each other) in a host of ways. Relationships exist all around us and can range from conceptual to the more tangible (including physical). Relationships can be made with varying degrees of specificity, simply noting them as connected, identifying the nature (e.g., causal, negative) of the connection, and hopefully deconstruct the connection between two things into parts (i.e., identifying it as its own system). This cognitive act of distinguishing and deconstructing a relationship is a fundamental skill of systems thinkers.For systems thinkers, thorough application of the relationships rule can help mitigate problems caused by our bias toward identifying structural parts and ignor- ing dynamical, interacting ones within a system (Forrester, 1971). It is the dynamic relationships between and among things that generate much of the complexity seen in systems of all kinds. Nonetheless, one often studies a system by isolating and overly focusing on the structural parts and neglecting the more complicated, dynamic features. The important systems thinking concept of emergence is a good example. It is often said that “the sum is greater than the parts” (Capra, 2002) but this is only true when one neglects to consider the dynamic interaction among the parts – the relationships – of a system.