But here you refer to implementation details. Isn't the point about message passing that objects themselves communicate with one another through such messages? And in turn, messages can also be assumed to be small objects. I don't think any of those implementations really fulfil that as a meaning. Or perhaps I misunderstood Alan Kay here. He drew inspiration more from biological cells and communication pathways therein. Naturally biology can not be mapped 1:1 onto in-silico hardware, that wouldn't even make sense either - but for instance, erlang's model appears to me closer to different objects happily communicating with one another in a very flexible, safe, fault-tolerant manner. I don't think it is the implementation detail that is about message passing. I also don't think "sending a message" is the confinement either - it's an important but, but does not appear to capture all that is meant with a "message". A message could be many things, including objects that themselves could change at any moment in time again. I see it more as an intrinsic part of communication at all times.