The condition of truth is the possibility of writing, that is, of a material inscription.
Rather than this inscription (mis)reflecting the truth—the argument which institutes ‘logocentrism’—its possibility is constitutive of truth as such. Thus, for Derrida, metaphysics constitutes its oppositions (the non-worldly/the worldly, the ideal/the material) by expelling into one term of the opposition the very possibility of the condition of such oppositions.
Derrida calls this general possibility of inscription arche-writing.
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See that post with different algorithms in metabole