"Naivete" is lack of wisdom, judgment, sophistication, experience. "Naive realism" (a/k/a direct realism) is the view that those things we deal with every day, indeed every instant, taken for granted by all but philosophers and their students, are perceived by us immediately or directly. Naive realism is apparently referred to as "naive" disparagingly. It is, after all, the view typically taken by most of us, the untutored common folk, as a matter of common sense (I would maintain that it is for all practical purposes the view actually taken by those of us who consider themselves uncommon, as well). Being so very common, it perforce is invalid according to those sophisticated in theories of knowledge and perception.
I find myself wondering, though, whether those who disparage naive realism are themselves naive, and whether their disparagement of it is a result of their own naivete.
We began to insert (as it were) something between us and the "external world" some centuries ago, for reasons I find difficult to understand. It may all have begun with Descartes' insistence on the use of faux doubt to establish knowledge. It may have begun with Hume. It may have begun earlier, but I think not that much earlier at least as far as the modern forms of insertion as we know it are concerned. Since ancient times there has been a tendency among the wise to doubt the quality, worth and even in some cases the reality of the universe--especially those parts of it that are not human--and it's possible the more modern reliance on sense-data or qualia to separate ourselves from the non-human, and perhaps our fellow humans as well, is an outgrowth of this tendency. But if that is the case those who more recently doubt what the common folk believe are more specific in their doubt.
It's claimed philosophers frequently ask why we should believe what we believe. Lawyers are known to ask why we do as well, but in my case and in this post I ask why philosophers (some of them, in any case) disparage naive realism. For me, the old claims that we have reason to doubt the veracity of our senses because of hallucinations, sticks in water and such, are unimpressive. J.L. Austin pretty well laid waste to those claims, as far as I am concerned; but there is also the fact that our senses seem to serve us very well in most cases. Not being committed to a need for absolute certainty, I think our successful interaction with the rest of the world in most cases indicates our senses function quite well in perceiving the various "external objects" we cannot exist without. Then again, the fact that, e.g., the perceptions of people who are distant from something may differ from those close to it is something I find unsurprising. I'm inclined to believe that such differences are more the result of distance than anything else.
But I suppose it is the fact that we cannot exist without that portion of the rest of the universe with which we interact which makes me wonder why we're inclined to separate ourselves from the rest of the universe in this fashion and in other respects. We're living organisms and like other living organisms we've been formed by our interaction with each other and the rest of the world over time. As we are part of the world, the idea that we are incapable of knowing what other parts of it really are doesn't make much sense. If we didn't have that knowledge, we wouldn't exist. Of course, there's much about the universe we don't know, and our knowledge in some cases is based on instruments we create or inferences we make. But it doesn't follow from these facts that we in all cases cannot experience the rest of the world as it exists apart from us.
Perhaps those who disparage naive realism suffer from their own lack of knowledge and wisdom. They seem to believe that we are in some sense detached from the rest of the world, different from or superior to a living creature in the world. They fail to recognize our dependence on the world, being convinced that the world is dependent on us, an astonishingly unsophisticated, parochial view given the vastness of the universe.
It isn't necessary to posit the existence of sense data or some kind of "representation" of what's out there to explain or justify perception or knowledge. It is necessary, however, to recognize what we are as creatures of the universe. We have our limitations, but such is to be expected; to expect otherwise is to claim and seek for a godlike ideal of perception or knowledge. We perceive and know just as human beings, formed over time through evolution, are equipped to see and know. The fact we don't perceive and know as other creatures do merely means we're human and they are not. It doesn't mean that there is something between us and the rest of the universe on which we're fated to rely.
If there is such a thing as sense data (or whatever) which is what we experience directly, it would seem that is the case for other creatures as well. So presumably other creatures are similarly incapable of experiencing the world directly, perhaps even less capable than humans, being less sophisticated organisms. All living things incapable of immediate experience of the universe, yet living in it. It's a remarkable belief indeed.
Of course, the claim is sometimes made that we can know enough about the rest of the world, or can rely on our perception, just enough to survive and function, but even so we cannot know fully what "external objects" are or what characteristics they really have (or if they are?), being limited to that something or other, the insertion, which is all we can experience. But that is to say that there is a difference which doesn't make a difference, and so is no difference at all as William James said as noted in a different post.
We test the precision with which our senses function as we must test everything, by judging the results of our interaction with the rest of the world. There is no other justification for our knowledge and perception. But our interaction with the rest of the world establishes that our perception of it
is valid enough for there to be no concern, except perhaps for those who are naive enough to think otherwise.