A second feature the reader will encounter at several points in Marsilius’ works, and which also foreshadows the ‘‘Wegestreit,” is the sharp distinction between faith and natural reason. This occurs not only in his theological works, but also and especially in his commentaries on Aristotle. At several places in these commentaries, Marsil-ius juxtaposes two different answers to one and the same problem, the one according to Aristotle and natural reason, and the other according to truth and faith. He leaves no doubt that for him truth and faith gives the right answer and should judge Aristotle and natural reason, not only in theology, but also in philosophy. Yet this does not prevent him from carefully setting out what should, according to natural reason, be regarded as possible or impossible in each particular case, even if this is in opposition to faith. Nor is his approach to these two views in his commentaries on Aristotle always the same. In some cases both views are dealt with extensively, in others he merely comments that according to faith things are different, but that he would not enter into the view of faith, as that was not the task of the philosopher, but of the theologian.
For Marsilius, natural reason is human thought based solely on sense-perception (experientia) and on selfevident principles (principia per se nota). To him this is essentially identical to what Aristotle said in his writings, for example, that nothing can come from nothing. Only very rarely are there instances in which he criticizes Aristotle for saying something not in agreement with sense-perception or self-evident principles — most prominently, in the case of the theory of movement, as we will see below.
The juxtaposition of the views of natural reason (Aristotle) and of faith occurs so frequently, both in his philosophical and theological writings, that it indeed seems programmatic. This is most clearly observed in his Abbreviationes librorum physicorum, which were written in Paris (as can be deduced from examples in which he repeatedly referred to the towers of Notre Dame and of St. Genevieve). In this treatise, both views are often presented in different sets of statements intended to make clear what their presuppositions are and under which conditions they could be accepted. A good case in point is the discussion of the eternity of the world. Here, Marsilius begins with a number of statements accepted both by Aristotle and by the believer. He then continues with statements held by Aristotle and rejected by the believer, such as that the movement of the heavens is eternal. At the end of this list, he remarks that although these statements must be accepted by all who use only the senses, nonetheless, the opposite is in fact true, as faith maintains.
Marsilius also follows this procedure in his discussion of other topics in the Abbreviationes librorum physicorum. For example, he argues that for Aristotle and natural reason (1) creation from nothing is impossible, (2) the first principle cannot act on earth without the assistance of the heavens, (3) an imaginary space outside of the heavens must be infinite, (4) the existence of a vacuum cannot be accepted, (5) the heavens cannot move faster than they actually do, (6) the first principle has no infinite power, and (7) the first principle is not everywhere. On all of these points he explains that faith, since it accepts divine omnipotence, asserts a differing or opposite position. Remarkably, for Marsilius, natural reason alone is not able to accept the position of faith. It must indeed reject all of those views that would presuppose the existence of something beyond sense perception and self-evident principles.
To be sure, Marsilius did not defend the theory of double truth. For him there is only one truth, namely, that of faith, which partially, but not completely, covers the claims of natural reason. However, and this is crucial, natural reason cannot judge on its own whether that which it necessarily has to accept according to its own principles is also true. To do this, natural reason requires faith. Marsilius therefore maintained a position which was very different from that, for example, of Thomas Aquinas. According to Thomas, regarding any tenet of faith whatsoever, natural reason can at least show that it is not impossible. For Marsilius, natural reason cannot do this. On the contrary, at crucial points it leads human reason in the opposite direction.
In his commentaries on Aristotle, Marsilius does not discuss the background of this radical view. His commentary on the Sentences, however, provides a clue. As a consequence of the Fall, human reason is bound to the senses and can no longer by itself give a sound judgment of what is true. Its evidence is evidence of the bodily, fallen man, not that of the spiritual man assisted by divine grace.
Marsilius defended his reading of Aristotle not only in Paris, but also in Heidelberg, as can be judged from his commentaries on the Metaphysics and the Sentences, both of which were composed in Heidelberg. Testifying to his influence as rector there, this interpretation of Aristotle found its way into the vows the masters were required to take at their inception. At most other universities, the master was obligated to refute, to the best of his ability, those of Aristotle’s opinions that were contrary to faith. However, in Heidelberg the situation was different. There, the master was required to tell students that in such cases, the position of Aristotle was based solely on natural reason and therefore was deficient, although his position could not be refuted, since using sense-perception and selfevident principles one must necessarily reach the same conclusion as Aristotle.
This way of dealing with Aristotle was to become typical of late-medieval Nominalism, for which Marsilius was one of the main sources of inspiration. It provoked harsh criticism especially from the Thomists, who were of the opinion that, principally, there were no points on which Aristotle was against faith, provided that he was understood correctly — which is to say, in the manner of Thomas Aquinas. Herein is rooted the historiographical myth that Nominalism destroyed medieval Scholasticism by questioning the harmony of faith and natural reason (Aristotle).
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