This article investigates Agamben’s conceptual reworking of the famous Hölderlinian expression “the free use of one’s own is the most difficult thing”, indicating in the original Greek matrix of the key term – i.e. the idion inscribed in the semantic genealogy of “Eigenes” –, the possibility of a deeper understanding of the Hölderlinian expression. The conceptual polarities of “appropriation” and “expropriation”, of “proper” and “inappropriable”, as well as of “style” and “manner” run throughout Agamben’s work, representing one of the most significant points of confrontation between twentieth-century philosophy and Hölderlin’s aesthetic reflection. The “secret” of the “appropriateness” is identified with the concept of idion, which activates a semantic constellation of great interest to speculatively understand Hölderlin’s “formula”. Thanks to Zanzotto’s poetological mediation, the “truth” of Hölderlin’s reflection – and Agamben’s use of it – proves the philosophical understanding of the idiomatic dimension of language.