One of the greatest strengths of the "traditional" view of theology (Patristic and Scholastic) is how the category of knowing which is "faith" is intrinsically related to the category of knowing which is "reason." This is the gist of the famous line that theology means "faith seeking understanding." All truth leads to Truth, therefore, and Truth must necessarily be one and universal.
These ideas about truth, knowledge, and so forth are not merely unprovable assumptions, for which other (equally valid because equally unprovable) assumptions might be substituted. Rather, they rest on a long tradition of observation, analysis, testing of hypothesis, and synthesis. They are proven, at least at the level of plausibility and self-coherence. They have stood the test of time (despite the contempt that modernity's irrationality holds them in). They are, in effect, conclusions of "natural theology."
Take, for example, the problem of defining "life" in "living" objects, as opposed to non-living objects. Reason tells us that the stuff is the same - the same elements of hydrogen, carbon, and oxygen, merely arranged differently here than there. Reason tells us, however, that there is clearly something different between living and non-living things. If you've ever seen a person or an animal die, you know that the difference is clearly visible, but not clearly quantifiable. Metaphors like "the light in the eyes" must be employed. In fact, reason tells us that the difference between living and non-living is not really a question of the arrangement of stuff (atoms, molecules) at all. It's something different.
In other words, experience, observation, and reason clearly "prove" the existence of something non-material. Its effects are observable; it itself is not directly observable. In terms of living objects, this non-material element can be called "soul." It expresses the vitality, motion, and ultimately rationality of different kinds of living things. But it can never be reduced only to material properties.
Coming at the problem from the angle of faith works essentially the same, but in reverse. The same observations about the material world, and the visible effects of the spiritual world therein, describe different kinds of relationships with God. Here "soul" is not a property or set of properties related to the observable differences in categories of objects, but defining spiritual realities that separate those same categories of objects in how that relate to God.
But these two aspects of the idea of "soul," from reason and from faith, are not to be seen as unrelated to each other. Together, they tell us more about "soul" than simply the juxtaposition of the two ways of knowing.
But for this to be true, that spiritual knowledge must be expressible in the form of a proposition (or more likely, a set of propositions). Even if the set of propositions is not complete in an absolute sense, it still must be relatively complete (relative to the extent of our ability to know at all), and accurate to the same extent. If this is not true, then "faith" knowledge is not related to "reason" knowledge, since the rules of logic (that is, propositional relationships) don't work there.
This is the heart of the propositional model in Dulles's schema. Of the five, only this model holds the intrinsic relationship of faith-knowledge and reason-knowledge; that is, that revelation is ultimately reasonable in itself. The historical model, and Dulles's theory of symbolic mediation, hold an extrinsic relationship between faith and reason. This can, in practice, be fairly close to the intrinsic relationship, but it's not really the same idea. At root, the existential, dialectic, and transcendent models all separate faith and reason from each other in modernist ways; this is why they are less successful at grasping revelation.
This is why I insisted in the previous post that there must be some non-ambiguous "rule" - an act, a word, or a symbol; or a combination of these, as in Exodus and the Passion - at the bedrock of revelation, prior to the mediation of the symbol(s). This "rule" must be expressible (to the extent of human knowing) as complete and accurate propositions. Even if the propositions are derived, and not taken as the primary content of the revelation itself, still the propositions are equal to the revelation in its relationship to the faith community: the propositions carry the revelation. I mean this concretely, not abstractly, because the propositions are not simply abstract, but concretely embedded in the liturgical life of the community (Passover and Mass, etc.). They are still explicit, however: they are acts, words, and symbols expressible as propositions. Therefore the meaning is not ambiguous and subject to change, and not derived from human sources, but given by God.
It is precisely in the knowing by both faith and reason that the certitude of revelation exceeds that of science (reason alone) or of individual inspiration (faith alone). It is precisely in the being carried by Tradition that the meaning remains stable and non-arbitrary. And it is precisely in the "faith seeking understanding" that we accept the invitation into God's own life, which is what revelation really is.