The cognitive learning processes of assimilation and accommodation are critically examined in this paper. A special focus is given to an analysis of the process of assimilation as it is proposed in Hugh Petrie's book, "The Dilemma of Enquiry and Learning." Initially, Piaget's biological metaphor of assimilation-accommodation is reviewed and then is followed by a discussion of a new metaphor drawn from the field of cybernetics. A control systems metaphor is described and compared to the process of assimilation as a special case of rule following. It is suggested that teachers and scholars use Petrie's model of accommodation to explain both of the learning processes, for in this model the learner continually tries to fit sensory inputs into an existing set of conceptual schemes. (ML)