In order to maximize impact, and to clearly convey the Big Clue, I have deliberately simplified the picture presented in "RAW Bits - and Credo".  Since I suspect few are interested in these "details", I am appending them here under a false date and time to prevent them from driving away new readers.  The following, in short, may be a little dry.

A great deal about us cannot be attributed to the effects of experience, or even of reflection, but must necessarily be attributed to inherent properties of the human nervous system.  If Kant is to be believed, many of these are necessary preconditions for the existence of any  individuated conscious mind.  In any case, we do manifestly have them, and in some cases the neural infrastructure is fairly well known, or in the process of being investigated.

Regarding that cabbage, it is fair to say that its cabbagehood and the matrices of import in which that quality is embedded are, as claimed, learned.  However, much of the construction of that object is due to inherent mechanisms.  We come into our lives with significant brain structures devoted to language, and to perception.  Associated with these are inherent functions of reasoning, and, as it were, of world-mapping.  We necesssarily experience the world in space and time.  This immediately implies such concepts as location (and associated with this, distance, size, shape, etc.), sequence, simultaneity, and (arguably) causation and explanation.  Language in particular requires the capacity to oganize perceptions under concepts, to divide the spatial field into discrete objects, to attribute properties to these, and to conceive of matters in terms of structures and processes.  And let's not forget identity, similarity, affirmation, negation, number, and difference.  (And there are others!)  All of this is largely pre-reflective, and already built into our immediate perceptions, quite apart from any learned interpretive framework of the sort I attribute to "Shepherds".  Reflection, an important component of which is reasoning, also supplies us with widely-applicable conceptual tools such as consistency and implication, which also severly constrain us - though this can hardly be seen as a bad thing!  Again, no "Shepherds are required for this.

A major task for the best sort of "Good Shepherds" - philosophers - has been the careful delineation of best practices for the construction of our individual and culturally-shared "worlds".  A broad consensus among the better contemporary epistemologists such as Quine (referred to in the original post) provides an attractive account of the better sort of world-making, which importantly constrains the excavation of reality tunnels according to minimal, but strict, standards of rationality (like consistency), which govern not only the internal relationships between our various ideas, but also the relationships between our internal map of reality and the ongoing stream of sensory experience.  Fully embracing modern science as embodying our most refined - and successful - forms of knowing the field of experience, they provide a robust model of revision and reorganization of our "world" which allows us to continually or periodically rebuild our reality-tunnels.  Since this rebuilding is constrained by the direct evidence of experience, by the careful incoporation of observations by others, and by those logical constrants whose abandonment would make any  type of world-building completely arbitrary, it is reasonable to suppose that a world constructed according to this plan is as close as possible to the presumed objective order underlying our sensations and our inner lives.  (It should be noted that the incorporation of others' observations is, itself, subject to the constraints provided by direct experience and reasoning, which provides some protection against "Bad Shepherds".)  The assumption of an underlying order is, perhaps, unfounded, but without it, there is actually nothing left for us to do at all, and so, in order to be able to conduct our daily affairs (like buying cabbages at the grocery store), we have to go with something - and this is the something we have.

Triangulating between these observations, and those in "Raw Bits", it is clear that we are still very much in the thrall, first of all of our hard-wired mental structures, and secondly of the "Shepherds" of whatever Fold we find ourselves in.  Nonetheless, we have quite a bit of room in which to manoeuver.  For all that the "philosophic" model provided above may seem to commit us to dull and relatively conservative "reality-tunnels", the sheer fact of the matter is that not one in a thousand people actually tries it  to see what results obtain.  These are in fact quite radical, as many common conceptions will not survive this trial by fire, and many matters commonly considered uncontroversial are revealed as so far unsettled - thereby requiring suspension of judgement, and gifting us with the sort of opened mind that can with great excitement freely expect that even the most remarkable things may yet happen, and that even the most outlandish claims may yet be true.

Or kill me!