Plato's explanation of why the deepest truths cannot be expressed in written form is famously abstruse. Before one attains the "thing which is cognizable and true" ("gnōston te kai alēthes"), one must have apprehended the "name," "account" ("logos"), "image," and "knowledge" ("epistēmē"). Name and account are approached through verbal description, while sense perception perceives the image. One attains knowledge only from the combination of verbal description and sense perception, and one must have knowledge before one can attain the object of knowledge (which Plato calls simply "the Fifth," name, account, image, and knowledge being "the Four"). The Fifth, moreover, differs from what is sensible and verbal expressions of it. Name and account provide the "quality" of a thing ("to poion"), but not its "essence" or "being" ("to on"). They are, moreover, akin to sense perceptions in that they are ever shifting and relative, not fixed. As a result, the student who attempts to understand the Fifth through name, account, image, and knowledge is confused; he seeks the essence, but always finds the quality intruding. Only certain kinds of student can scrutinize the Four, and even then the vision of the Fifth comes by a sudden flash.