Metaphysics and Ontology V

The Question of Demonstrative Science

Like all medieval theologians, Luther was well-educated and very interested in logic.  He knew his Aristotle very well, lecturing on the great philosopher when in graduate school.  It is thus important that we know something about Aristotle's views on demonstration if we are to get clear on what Luther is doing in his more technical work where he thunders against "a logic of faith."

Aristotle argued in the Posterior Analytics that the deepest scientific knowledge of a thing required that thing to be grasped in terms of its necessitating causes.  Accordingly, the demonstrative syllogism produced the deepest knowledge (Eileen Sirene, "Demonstrative Science," in Cambridge History of Later Medieval Philosophy, p. 497).  Through such a syllogism knowledge of the fact was established (demonstratio quia) as well as knowledge of why this fact must obtain (demonstratio propter quid).

Toward the end of the first quarter of the 13th century, Robert Grosseteste became the first in the Latin west to comment on Aristotle's entire Posterior Analytics.  While he agrees with Anselm and others that the truth of a thing is its conformity with the rationes in the divine mind, he holds that the truth of a proposition is found in the conformity between what the proposition asserts and what is the case (Sirene, p. 502).  Grosseteste's commitment to a theory of divine illumination affects his interpretation of the Posterior Analytics.  While Aristotle indicated that experience and induction lead to an intuitive grasp of first premises in demonstrative proofs, Grosseteste grounds first premises in a "direct or indirect irradiation of his mind by divine light" (p.503).  Without such illumination no certainty is possible.

Aquinas downplays illumination as a necessary epistemic feature of this life, claiming with Aristotle that we can grant first principles and definitions through experience.  As it turns out, Aquinas assigns to the role of demonstrative science a small subset of the set of all truths, for most of what we claim to know is opinion, not scientia.  The latter demands both demonstratio quia and demonstratio propter quid, something lacking in the former.

Scotus relaxes the Aristotelian requirement that knowledge of something demands that one know why it necessarily happens.  Because of his commitment to the potentia dei absoluta, Scotus denies that knowing x presupposes that we know why x must be what it is.   The fact that it is an x is completely consistent with the possibility God could have willed ~x.  Scotus thus changes the nature of demonstrative science from the project of discerning what is necessary in nature to finding instead what is possible or compossible within it.  This has repercussions for his theory.  While demonstrative science could establish the connections among general truths, it is incapable of explaining why this particular was instantiated at this particular time.  This cannot be proved because God could always have changed his mind and not brought that particular into being. Here as elsewhere, voluntarism seems to push towards nominalism and the contingency of the individual.  

The great architect of the via moderna, William Ockham follows Aristotle in claiming that better known premises provide warrant to affirm the truth of those propositions entailed by them.  But, he realizes that "the resulting sciences are collections of true propositions, and not necessarily a mirror of the inner constitution of nature" (p. 513).  They can be only contingent propositions because God is the only necessary being.  Ockham does say that knowledge acquired by demonstration is not different in kind from knowledge by experience (p. 514), but understands this to mean that demonstrative knowledge needs to presuppose experience, not the other way around.  Jean Buridan follows Ockham on the difficulties of establishing an Aristotelian demonstrative science of nature, holding instead that such reasonings must allow for linking propositions which are almost always true with others of the same kind (p. 517).