Aristotle's accounts of the five senses can concentrate upon their proper sensible objects and the way they operate through a medium and sense organ. Since he has already developed a general account of a sense faculty in ii 5.418a3–4, “The sense power is in potentiality the sort of thing the sensible object is already in actuality,” all that is needed to develop a definition of a particular sense is insertion of the sensible object. For example, vision is in potentiality the sort of thing the visible object, that is, color, is in actuality. Similar accounts readily apply to the other senses (see esp. 422b15–16). Hence these definitions do not receive much explicit formulation. Instead Aristotle concentrates on what the sensible object is and how the sensory apparatus including the medium and sense organ permits the operation of sense perception such that the sensible object can be perceived as it is. Thus he justifies his general understanding of sense. Since his general account of sense is open to many objections from the phenomena of the particular senses, Aristotle, wishing to make his case as strong as possible, introduces these phenomena to show that they fit his account. Hence each of the proper senses is treated for its own sake and for sustaining the general account of sense, to which ii 12 returns after the chapters on the five senses.