Alexander Calder is known for his “mobiles” and “stabiles”. Before him, no one knew that a “mobile” was a sculpture in motion. We owe the term to Marcel Duchamp. Calder recounted the scene as follows: “There was an object with three elements. The object had just been painted and was not yet dry. Marcel said to me: ‘May I?’ He put his hand on it and the object appeared to please him (…) I asked him what I should call these objects and he immediately said ‘mobile’.”