Each curried function returns a new function that closes over the previous arguments. The inner function has access to all outer arguments via the closure. Without closures, currying would not work.

Closures provide the accumulated arguments (state) across calls. Each returned function remembers the previous arguments via the closure. Without closures, the inner function would not have access to outer arguments.

The returned arrow function (...next) => curried(...args, ...next) closes over args and fn. Each partial call accumulates arguments via the closure. When enough are collected, fn is called.