This paper presents a cybernetic theory of conversational interaction and describes one embodiment of that theory CASTE (Course Assembly System and Tutorial Environment). The work which has led to the present development of the theory has been amply represented in the literature; in particular Lewis and Pask [65], Pask, G. “A Cybernetic Experimental Method and Its Underlying Philosophy” Int. J. Man-Machine Studies (1971, 279-337) and Pask and Scott [64, 65]. These papers describe some of the work on adaptive teaching and training methods which served as an impetus for the present research.