You're quite right -- take a look at the original 1973 paper [1], "A Universal Modular ACTOR Formalism for Artificial Intelligence". The "universal" there is in

You're quite right -- take a look at the original 1973 paper [1], "A Universal Modular ACTOR Formalism for Artificial Intelligence". The "universal" there is intended to mean, among other things, a uniform actor model (comparable to the uniform object model in Smalltalk). It's a remarkable paper. Later actor languages step away from total uniformity, in part because it requires quite some finesse to avoid infinite regress and/or great inefficiency in such a system. [1] https://eighty-twenty.org/2016/10/12/hewitt-bishop-steiger-ijcai-1973 https://eighty-twenty.org/2016/10/12/hewitt-bishop-steiger-i... A few choice quotes from Hewitt, Bishop & Steiger IJCAI 1973: "An actor is always invoked uniformly in exactly the same way regardless of whether it behaves as a recursive function, data structure, or process." (p235; page 1 of the PDF) This implicitly includes messages. "The intentions [roughly, contract monitors] are written in the same formalism as the procedures they describe. Thus for example intentions can have intentions." (p235) "[The reader] might envisage an infinite chain of actions (such as banking) to be necessary in order to get anything done. We short circuit this by only requiring that it appear that each of the above activities is done each time an actor is sent a message." (p238) "There are no instructions [in the sense of present day machines] in our model. Instead of instructions, an actor machine has certain primitive actors built in hardware." (p241)