Relation. The means by which structures cohere, where relations are established between kinds of things, parts of things, properties of things, and things that cause. But, despite our capacity to generalize relations, no two structures are the same, and no two relations within these structures.

Reference: Cope, Bill and Mary Kalantzis, 2020, Making Sense: Reference, Agency and Structure in a Grammar of Multimodal Meaning, Cambridge UK: Cambridge University Press, p. 307.