The paper aims to clarify the concept of possible worlds developed by Leibniz established when the debate in his correspondence with Arnauld. Leibniz conceives different worlds that could have different laws and primitive notions of order from what he calls other possible free decrees of God. It is to solve the problem of freedom and determination that Leibniz will propose the intriguing concept of worlds as different order types according to the different divine plans. Our goal is to understand this concept of physically possible worlds.