In these pages the author intends to examine the idea, quite widespread among Aristotle’s recent scholars, that the method of metaphysics were mainly dialectical. This problem is investigated in Aquinas, who decidedly denies that metaphysics uses dialectics because it just provides probability. Metaphysics, unlike dialectics, is not only based on the being of reason but also on the natural being. Therefore, it does not simply constitute a rational game about quiddities, but it studies things in their real actuality and must (...) therefore be supported by evidence. Although Aquinas agrees with Aristotle in affirming that not every science enjoys the same certainty, this fact is due to different reasons. First, all things do not possess the same stability and constancy. Secondly, there is not always a perfect match between the studied matter and the human faculty to ascertain. This match between the object and the subject is the most decisive factor for the certainty of sciences. (shrink)