Mary Douglas, a British Functionalist, extended Turner's theory of ritual structure and anti-structure with her own contrasting set of terms "grid" and "group" in the book "Natural Symbols". Drawing on Levi-Strauss' Structuralist approach, she saw ritual as symbolic communication that constrained social behaviour. Grid is a scale referring to the degree to which a symbolic system is a shared frame of reference. Group refers to the degree people are tied into a tightly knit community. When graphed on two intersecting axes, four quadrants are possible: strong group/strong grid, strong group/weak grid, weak group/weak grid, weak group/strong grid. Douglas argued that societies with strong group or strong grid were marked by more ritual activity than those weak in either group or grid (see also, section "Ritual as a Methodological Measure of Religiosity" below).