This paper aims at questioning Berkeley's formula: « I am not for changing things into ideas, but rather ideas into things » (Three Dialogues). It shows that the identification of ideas with things is a consequence of immaterialism and constitutes a decisive element in the fight against scepticism. The very being of the thing is now decided on the basis of thought. Berkeley is often presented as a thinker who breaks with the philosophers before him. If this view is right, (...) it is also incomplete. We show that the identification of the idea with the real thing represents the culmination of speculations born during the Middle Ages, and repeated in cartesianism itself. (shrink)