You are on to something with ”behaviour”, ”actors”, and ”rational” . Ludwig von Mises defined ”rational” as ”aiming to an end, using means”. That means that even someone performing a dance to produce rain is a rational actor. He formulated the axiom that ”humans act”. And then derived his theory from that. The science is named Praxeology. A big difference from the natural sciences is that you really can't falsify a theory using empirics. There is no way to repeat an experiment, because reality has been reconfigured. Therefore axiomatic theory is what you have to rely on. Which is not too bad. After all sciences like geometry also make do without empiricism. (There is no way to empirically disprove that a triangle has an angle sum of 180 degrees.)