The contextFor property states that one observation serves as the context for another observation. In the case of contextFor, the domain is the context, and the range is the observation being contextualized. Context defines a semantic relationship between two entities that is a fundamental aspect of the observations, but not necessarily of the entities themselves. For example, most measurements are accomplished in a spatio-temporal framework that might be valuable context. The assertions made by contextual observations are assumed of the contextualized observations. Context is a transitive relationship.