  The so-called regressus-method is a model for combining composition and resolution: the idea of this combinatory process is found in the Aristotelian tradition from Averroes on, and it was vitally revived among the Italian Aristotelians and medical authors. According to this method, the natural philosopher should first infer from the known effect the existence of the cause of this very effect. Sometimes he may use induction, but usually resolution, which was also called demonstratio quia or demonstration from the fact. Then in the second step, in the so-called demonstratio propter quid or demonstration from the reasoned fact (or composition), the natural philosopher should infer from the cause to the effect. The effect is now known through its cause, and hence in a scientific manner (Risse 1983). The crucial problem with this procedure is how to avoid mere circular reasoning, or rather, how to make sure that the cause, whose existence is demonstrated in the first step, is indeed the cause of this very effect. From the beginning of the sixteenth century, it had become clear that it was necessary to introduce a third, intermediary step, which involved some kind of intellectual consideration (negotiatio intellectus) (Kessler 1998, p. 838).