[1] Plato's Phaedrus ends with the myth of Theuth. In this myth writing is offered as a kind of present to King Thamus. The king, who in fact represents Ammon, king of the gods, receives this gift from the demigod Theuth. But it is the king who will give this gift its value in the act of receiving or rejecting it. According to Derrida, '... the value of writing will not be itself, writing will have no value, unless and to the extent that god-the-king approves of it' (Dissemination, p.76).
King Thamus does not know how to write and he has no need to write. He speaks, he dictates, and his word suffices. If a scribe writes down the words spoken by the king - a supplementary transcription - this is always in essence secondary. Writing is secondary. It comes after speaking.
God-the-king rejects the offering of writing; he does not need it and prefers speech, or logos, above writing. Writing does not produce truth. It does not produce anything; rather, it reproduces. 'Written logos is only a way for him who already knows to remind himself of the things writing is about. Writing thus only intervenes at a time when a subject of knowledge already possesses the signifieds, which are then only given to writing on consignment' (Dissemination, p.135). This is the difference between knowledge as memory and non-knowledge as rememoration, a repetition of truth versus a (dead) repetition of the repetition. Writing stands for an oblivion that veils. Presented in a simple dichotomy, logos thus means presence, the good or the true, whereas writing can be associated with absence, the bad or the untrue.

[2] Plato understood writing as a sign of a sign, that is, a sign of the spoken word that, in turn, is the sign of a meaning that is expressed. Writing is therefore a two-step representation. It is in the service of logos as the living speech act. Writing is an exteriority that is subsequently added to the inner purity of the concept, the essence, the signified, the soul, the spirit. Since writing can only repeat, it does not add anything essential and could therefore be considered unnecessary. Nevertheless, Plato presents writing as dangerous and threatening. Writing is dangerous because it kills the living meaning and presence of the consciousness to itself; it forms a threat to the inner purity.

[3] Derrida draws our attention to the fact that Platonism assigns the origin of logos to the paternal position. The speaking subject can be conceived of as the father of his speech. Speech or logos is his son. The specificity of logos would thus be intimately bound to the presence of the father. Logos is alive because it is inspirited by its father (the one who speaks), who can constantly explicate, supplement, explain, etc. The spoken word is not only positioned opposite writing, it is also considered superior because it is associated with presence, whereas writing may indicate a double absence (of both author and reader). The hierarchical relation that privileges the spoken word to the written word is based in the human desire for presence and origin. Writing is connected with the absence of the father. It is an orphan, a lost son. Writing no longer knows who his father is. On one hand, it escapes and undermines parental authority. On the other hand, it can be attacked, bombarded with unjust approaches. It is open to a multitude of misunderstandings and, in principle, an infinite number of interpretations that only the father could dissipate, thus assisting his son, if he was not absent.
The hierarchical relation might be clear: logos, living speech, is superior to writing, 'that dangerous supplement'.