If every call is an async message but the next step in your algorithm always depends upon the result/outcome of that async message you are programming a sequent

If every call is an async message but the next step in your algorithm always depends upon the result/outcome of that async message you are programming a sequential algorithm wrapped in concurrent clothing. I would claim that even if you use Erlang and distribute it across multiple processes your program doesn't actually exhibit concurrency. If you want to argue otherwise that's fine, but you just push the problem out: your program is "concurrent" but you gain zero benefits of concurrency, and when you distribute it across multiple cores to try to make it run in parallel it might be concurrent but by definition it will not be parallel. Either way you want to slice it you have a big problem with this line of thought. Edit: from my experience it is easy to write Erlang programs that exhibit something not exactly the same as, but similar to, this sort of behavior.