Peirce called an icon apart from a label, legend, or other index attached to it, a "hypoicon", and divided the hypoicon into three classes: (a) the "image", which depends on a simple quality; (b) the "diagram", whose internal relations, mainly dyadic or so taken, represent by analogy the relations in something; and (c) the "metaphor", which represents the representative character of a sign by representing a parallelism in something else.