Displacement

[1] The first moment of what may be observed as a deconstructive strategy consists of tracing a hierarchical opposition. In 'Plato's Pharmacy' Derrida describes how Plato assumes such a hierarchical opposition by stating that eidos (the father) precedes logos (the son). The father symbolizes the origin of logos. In the second moment, Derrida reverses the hierarchy by stating that eidos is not able to appear without logos. If the son is what causes the father to become a father, then the son, not the father, should be treated as the origin. By showing that the argument that elevates the father can be used to favor the son, one uncovers and undoes the rhetorical operation responsible for the ordering of the hierarchy and one produces a significant displacement. If either the father or the son can occupy the position of origin, then origin is no longer originary (cf. Culler, p. 88). This can be perceived as the third moment. Displacement. (Examples of displacements in music can be found in the sections on John Cage (Cage and Noise), J.S. Bach (Contrapunctus I), and John Zorn (Saprophyte).)

[2] Plato's Phaedrus presents itself as having no origin. It is merely the inspired conversation overheard by Plato between two men in the countryside. And recorded. Problem arise when we read the dialogue between Socrates and Phaedrus as a textual, not as a spoken construction, directed entirely by Plato. This is where the displacement of origin begins. For example, Socrates then becomes a (fictitious) character (cf. Neel, p.45).
To mask the origin of his thought as writing, Plato always uses the (prior) voice of another, in most cases the voice of Socrates. This allows Plato to remain absent, always and everywhere. Plato invariably makes his own monologue appear as a dialogue, usually between Socrates and another person. Plato can thus be considered both absent and present at all times. But this really applies also to Socrates. The voice of Socrates (he who does not write) lives in the absence of the voice of Plato (he who says he does not write), which in turn lives in the absence of Socrates' voice. The voice one hears is always the voice of the other. To make things even more complicated: In Phaedrus Plato uses a written speech by Lysias as the starting point for his own text. He assumes Socrates' voice in order to destroy the sophistical writing of Lysias. But it is almost certain that Lysias never wrote that speech. Plato did. Plato then gives up his own voice to two 'speeches' by Socrates (a displacement of Plato because he wrote them down) in order to destroy his own writing (the forged speech by Lysias) (cf. Neel, p.20). We are caught here in an endless chain of displacements in which the origin is lost or endlessly deferred.

[3] In Phaedrus, Socrates presents writing as the lost son of the father. This means that writing can be regarded as the brother, the bad brother of the good logos or speech. This brings Derrida to the conclusion that Socrates is led to the insight that logos is only another sort of writing, just because they are brothers. Socrates indeed perceives this in his statement that logos can be regarded as the inscription of truth on the soul. (Socrates: 'But now tell me, is there another sort of discourse, that is the brother to the written speech? ... The sort that goes together with knowledge and is written in the soul of the learner'.) Socrates thus calls the living, animate discourse an inscription of truth on the soul.
Logos as a sort of writing. Of course, we can disregard this as a metaphor. But it is nevertheless remarkable that Plato suddenly describes the so-called living discourse with a metaphor from an order that he is trying to exclude (cf. Dissemination, p.149). Truth, as Socrates says, is a kind of good writing in the soul. So writing, which has been pushed to the outside, marginalized, is now suddenly seen as being in the very heart of the interior. Plato saves writing by making it the medium for an internal journey toward truth. He resorts to the notion of 'writing in the soul' in order to name the other of writing, the self-present truth that speech is designed to convey. This throws the explicit opposition between speech and writing askew. Phaedrus, which starts as a condemnation of writing in the name of present speech, finally comes to light as a transformation into the opposition between two kinds of writing: good writing (natural, living, internal), and bad writing (moribund, ignorant, external). And the good one can be designated only by the metaphor of the bad one. For Derrida, this seems to be the conclusion of Phaedrus. Writing and speech have become two different species of one trace, which Derrida calls arche-writing (cf. Music Is a Text). A displacement of the initial hierarchy.

[4] In Sophist, Plato teaches that any full, absolute presence of what is, or any full intuition of truth, is impossible. This brings Derrida to the conclusion that truth or presence must always come to terms with non-truth and non-presence. The lack of attainment of presence or truth gives rise to a structure of replacements such that all presences will be supplements that are substituted for the absent origin, and all differences, within the system of presence, will be the irreducible effect of what remains beyond 'beingness' or presence (cf. Dissemination, p.167). Non-truth is the truth. Non-presence is the presence. This is what Derrida calls 'the movement of différance'. 'Différance, the disappearance of any originary presence, is at once the condition of possibility and the condition of impossibility of truth … What is, is not what it is, identical and identical to itself, unique, unless it adds to itself the possibility of being repeated as such. And its identity is hollowed out by that addition, withdraws itself in the supplement that presents it ... And there is no repetition possible without the graphics of supplementarity' (Dissemination, p.168). All this is inscribed within a generalized writing, an arche-writing. So on one hand, there would be no intelligible form of truth or absolute presence without repetition. But on the other hand, repetition is the movement of non-truth because in becoming apparent, in becoming perceptible for the senses, it withdraws from ideality. 'These two types of repetition relate to each other according to the graphics of supplementarity. Which means that one can no more 'separate' them from each other, think of either one apart from the other, 'label' them; that in the pharmacy, one can distinguish the medicine from the poison, the good from the evil, the true from the false, the inside from the outside, the vital from the mortal, the first from the second, etc. Conceived within this original reversibility, the pharmakon is precisely the same because it has no identity. And the same (is) as supplement. Or in differance. In writing' (Dissemination, p.169).
Truth and non-truth, presence and non-presence, inside and outside. Binary opposites in which the first term is the dominant one. Derrida subverts the hierarchical relation between the two terms; not by a simple reversal, but by showing that the opposition is unstable, by a displacement of the conceptual order.