What's Inside the Arrows?
Inside black boxes you find programs. There are a lot of programming languages. You may not care how black box \(A\) works as a substitute for black box \(B\) if it’s observationally equivalent to black box \(B\).
How do the boxes interact? What’s inside the arrows that connect the boxes? Inside arrows you find protocols. There are a lot of protocols.
Are you looking in the wrong place to see what’s going on? In practice, effort to understand e.g. English – the messages we send back and forth – is more fruitful and useful than effort to understand what’s going on in the brains of a system of people.1