The document discusses how applying object-oriented (OO) design principles can often lead to functional design when using Clojure. It provides examples of how single responsibility, interface segregation, and dependency inversion translate to more modular functional designs using namespaces, protocols, multimethods, and partial function application. Polymorphism in Clojure is more flexible than OO polymorphism through protocols and multimethods. State management can be modeled functionally using atoms to manage immutable state. Overall, Clojure allows embracing many benefits of OO and functional design together.