As much as I've disliked the phrase "the external world" (see below), I've long admired that last proposition of Wittgenstein's Tractatus, often translated (a bit sententiously perhaps) as, "Whereof we cannot speak, thereof we must be silent" -- followed by nothing. It has a teasing, mysterious, Zen-like quality to it, that may at least partly be due to the fact that it's paradoxical, or self-contradictory -- since the subject clause itself, brief though it be, speaks of that "whereof we cannot speak". And I don't think this is a mere quibble -- that very paradox illustrates an important understanding of both the limitations and the power of thought and its medium, language. There are some things which, by their nature, are beyond, or at least outside of, thought as such, but which at the same time, owing to the recursive, object-making nature of language, are "containable" by thought -- thought can hold them, in a fashion, even if it cannot reach them. And a very simple, mundane example of this is simply phenomenal experience itself, the stuff out of which thought is made.
But, speaking of what we cannot speak of, what about that "environment" mentioned parenthetically in the previous post as something altogether outside of knowledge, properly speaking -- should or can anything be said about it? The problem is that, once we're at the level of "saying" anything, we're immediately above the level of the foundation and into the social/cultural realm -- there is no way, in other words, of using abstractions like words that could ever get us "below" or beyond, in any sense, the basic level of phenomenal experience. But there is the word "environment" itself, after all (we could call it the "noumenon", or "external world" even, were it not for the representationalist baggage those terms bring with them) -- what can be meant by that? Suppose that we think in terms of two distinct contextual levels, an epistemological level and an explanatory (scientific) level. Then, on the epistemological level, given the epistemological inversion referred to in earlier posts, the "environment" simply names the principle that the world of conscious experience is a given, independent of conscious agency -- it isn't really a "thing" or "realm" at all, in other words. Within the explanatory level, on the other hand, when we're trying to formulate one of those efficacious "myths" that Quine speaks of (as, for example, in this blog generally), then it can be useful to think of the environment as an externality that stands in a determinate but possibly complex relationship to phenomenal experience. In this sense, and in this context, we could retain three different levels involved in language-based consciousness -- knowledge/belief (i.e., the cultural imprint), phenomenal experience, and environment, all of which are physical, all of which knowledge can embrace, but not all of which knowledge can be.