Whether delayed or not, reactions constitute what Piaget calls ‘subjective series’; they are gradually transformed into ‘objective series’, which differ from former in that the apprehended succession is objectified. When faced with a situation, the child no longer simply remembers his action, but also the object itself. The corresponding behavior is to seek a toy which has just disappeared behind a screen. Every parent knows that a baby will cease to want something if it is removed from his sight, but they also know that this possibility cannot last. Gradually the object has disappeared remains present through memory and baby no longer stops demanding it when it is not tangibly present.