tl;dr:“This post is meant as an explainer about how substructural type theory can be applied in programming language design. Terms like “substructural type theory” tend to scare and confuse programmers who don’t write Haskell on the weekends, so one thing programming language designers should do when thinking about how they will present their language is invent metaphors, even slightly misleading ones, to help more ordinary programmers understand how their language works. One such term is “ownership.””