"A somewhat lengthy and difficult argument"

Through a long argument, Republic 476e-480a distinguishes the true philosophers from the poseurs, the lovers of sights and sounds (LSS), as follows: The faculty of knowledge is over unchanging, eternal, and invisible objects, and the faculty of belief is over changing, temporal, and perceptible objects; thus, philosophers have knowledge of the forms whereas LSS (who deny the existence of forms) have only beliefs about sense-perceptible objects. (Plato claims that the only way to distinguish faculties is by what they produce and what they are over. His claim naturally develops from the way technai are defined in the Gorgias, but it conflicts with the method of collection and division in the Sophist and Statesman.) The difference between knowledge and belief is that knowledge requires the ability to produce an accurate explanation of the forms that represents them as they are on the basis of the knower's own character, thought, and experience. Forming true belief is a matter of believing what contributes to the preservation of the good condition of oneself, and the belief is "justified" if guided by knowledge. Because Plato says in the argument that knowledge is about `to on' ("what is"), the majority of interpreters focus on determining the meaning of the word `einai' ("to be"). However, the meaning of `einai' should not be the focus because Plato intentionally leaves the meaning of `einai' ambiguous. Thus, the argument needs to be reconstructed in two versions. One version expresses the premises as they are understood by Plato; on this version, `to on' is understood as "the forms." The other version expresses the premises as they are understood by LSS; on this version, `to on' is understood as "sense-perceptible objects." The difference between the reconstructions is that the Platonic version is valid but LSS version is not. Confronted with invalidity, LSS give up their claim to know. Plato gives an argument, instead of a myth, in order to persuade LSS because his account of the tripartite soul indicates that LSS are dominated by appetite, and those dominated by appetite cannot respond well to myth because it appeals to spirit.