Yesterday I had a Skype discussion with a fellow named Yaniv, who claims to believe in noumena, though by the term I suspect he means something dramatically different from what Kant and others have meant, historically. It is probably best to leave that word behind for now, and try to explain his view using different terminology. Yaniv suggested that we instead posit the existence of mind-independent things, or MITs for short, and that these are no less real than experiences or ideas.
Yaniv appears to accept part of Berkeley's argument against mind-independent objects. In particular, he agrees that mind-independence only ever makes sense in the context of a conceptual scheme, or model, which is of course itself mind-dependent. So although he wants to posit the existence of MITs, he doesn't make the mistake of supposing that MITs have some deeper existence apart from our mind-dependent models. Instead, he objects to idealism by denying that experiences exist outside those models either, so that MITs and experiences exist in precisely the same sense. In other words, for Yaniv, MITs appear to consist of the very "ideas" which Berkeley posited so many of us mistake for representations of mind-independent objects.
Assuming I have not misconstrued Yaniv's position, it seems to me that he has two options for criticism: First, he can agree, as he already appears to do, that MITs really are just ideas in the mind as Berkeley argued, but then also posit that ideas are in turn MITs, and on ad infinitum. However this would be a bold move, and not warranted by the evidence. For presumably he would want to say that ideas in the mind reduce to behavioral systems, or brain states, or something of that sort; yet while I certainly see a wealth of evidence connecting such systems with ideas, I see no reason to suppose that ideas are reducible to them. However let us assume, just for the sake of argument, that we are indeed convinced by this evidence. Even in that case, I do not think we would have sufficient cause to cast ideas in terms of MITs. For while it might it might always be in some sense possible for us to do so, it seems obvious that we do not in fact perform such reductions, at least not in most cases. In contrast, by hypothesis, MITs are in fact ideas in the mind. So even taking for granted the requisite evidence, this view still seems untenable.
This brings us to a second option for Yaniv: He can suppose that just like ideas may be in principle but not in practice reducible to MITs, so too it is not always the case that all MITs have in fact been reduced to ideas, even though it may always be possible to do so. However this seems quite implausible. For, given some MIT, this view requires that if none of us takes the time to actually reflect on the fact that this MIT is an idea in the mind, then it is not in fact an idea in the mind, which seems an impossibly high standard for what we take to really be the case or not. Yet here we run into a great danger, by inviting the charge of a double-standard. For just a moment ago we decided that ideas are not in fact reducible to MITs since we have not actually performed the reduction explicitly. If MITs are neither explicitly reduced to ideas, then is not this an equally-powerful objection against Berkeleyan idealism? In answer I can only say that the reduction of MITs to ideas seems more immediate and easily-performed than the supposed reduction of ideas to MITs. Indeed, we have not ever actually reduced any particular idea to MITs to my knowledge, whereas MITs are readily reducible to ideas upon very brief reflection. On the other hand, perhaps this judgment is too hasty; are MITs really so easily reduced to ideas? But to deny this seems again extremely implausible. For it would be tantamount to suggestions such as that, for instance, when I recognize that I have an idea of this coffee cup in front of me, I am not actually identifying the idea as such.
So I'm not sure what else is left for Yaniv. He can press the second option, perhaps, and argue that my sense of what is plausible or implausible ought not enter into our considerations. However I would have to wonder in that case if he really can make sense of ideas in the common sense not being ideas in a more explicit sense; certainly I cannot. Alternatively, he can deny that MITs are in any respect ideas in the mind. However this seems manifestly false, according to Berkeley's arguments, and indeed upon the briefest reflection.
Therefore I do not at this time feel compelled to abandon the Berkeleyan thesis that, in the current parlance, MITs are merely ideas in the mind, nor do I see any reason to suppose that ideas are always in turn MITs. In this way ideas do have special status as the only kind of real object, and so it is neither vacuous nor inappropriate to deny the existence of mind-independent objects.