You have described a fascinating phenomenon that I think is remarkably common, though I don't agree that it always happens It certainly happens frequently in my experience. Perhaps we both have very bright colleagues whom we happen to know very well, and can anticipate what they will say! I am delighted to see "the phenomenon" so well described. However, in the form you present it, I think most philosophers and psychologists would say that the question you ask is a psychological one, not a philosophical one, and that no doubt it is amenable to empirical research. Still, it does prompt a philosophical thought or two. I am put in mind of Wittgenstein's observation that 'In philosophy it is not enough to learn in every case what is to be said about a subject, but also how one must speak about it. We are always having to begin by learning the method of tackling it.' Perhaps when you ask a colleague about your problem, you have to decide not just what to say but how to say it, and that is enough...

My answer is a little different from Olilver's. Why do so many scholars and intellectuals think that language is necessary for thought? Answer: Because it really is easier to think about definite rather than indefinite things. But indefinite and formless things also have to be thought about. It takes more of an effort of course to think in a pathfinding sort of a way about something new, and one may or may not be thinking "in" language, whatever that means (muttering to oneself, sub-vocally?) If one is trying to come to an understanding of some hard and new logical or mathematical matter, it may be more like shaping forms in ones mind, and then moving them, and less like chattering in French. If one insists on calling "shaping forms", or whatever the metaphor is "a kind of language", then of course the claim is drained of any content, and with that of any interest. People of say that mathematics is a language, or a "language", something like a language. But it has a function and a status very different...

It is reasonably unclear what "mental" and "mind" mean overall, though it is clear that whatever it is the intellect is a central part of it, and so if some philosophers want to insist that the mind is to be taken as the conscious mind, there is nothing to stop them, and there is a reasonable point to their stipulation. But even as early as the turn of the 17c, Leibniz accepted unconscious thinking, and there is a very strong case to answer here. Not answering it can make the stipulation look very arbitrary. Locke died in 1704, by the way, and Berkeley in 1753, so they did not hold the view that you attribute to them "in the later 1700s". And Hume's philosophical writing was done early on in his career; the Treatise and the Inquiry were published before 1750.

If I dream that I am in Lisbon, it does not follow that I am, and I may not be. Nor does it follow that I am not, of course. But if I say that I dreamed that I was in Lisbon last night, this may be one way of saying that I was not in Lisbon. If then I say that I dreamed (in a "ground-floor" dream) that I dreamed something (in a second-level dream, so to speak), it seems to follow that I did not; I did not produce a dream within my dream. And it seems to me hard to see how I could. For the contrast is between dreams and reality, and there is no reality for the second-level dreams to return to. There are just sequences of images and dreamed descriptions of them. If I dream that I have a dream, the second thing I have is not a dream within a dream, but just part of the ground-floor dream.

Depression used to be classified in two forms: endogenous ("originating from within") and reactive. There was an obvious point to this way of classifying things, but a different way has been suggested recently. The newer way is to distinguish between cases in which depression, the medical condition, is present, with its bodily neurophysiological causes, and cases in which only symptoms of depression are present, and which lack the underlying neurophysiological cause. The symptoms might however be produced by some environmental cause, a depressing incident, a personal loss or a major setback in life, without the marked and persisting change in the biochemistry of the brain which is believed to underly the medical condition. The significant difference between the two kinds of condition seems to be that changes in the environment typically don’t touch the medical condition. That may even be a defining characteristic of the condition, as well the usual things doctors look for, such as failure of concentration...

"How can I hear my voice when I'm not speaking?" is your question. If we reserve the word "hearing" for what the ears do, and "the voice" for what the mouth speaks - not unreasonable, I think - then your question becomes, "How can I "hear" my "voice" when I'm not speaking?" i.e. "How can I undergo something which seems rather like hearing ("hear", in an extended or perhaps metaphorical sense) something which seems rather like my voice ("my voice", taken in an extended or perhaps metaphorical sense)? The important thing is to try to get clear about what the metaphors are metaphors on , if I can put it this way. ("The sun" is a metaphor on Juliet.) It is more than just imagination, because I can imagine a voice speaking, and hear it, without imagining that I hear it. That is, the minute the voice "speaks", I "hear" it, without an added act of imagination of the auditory (or rather, "atidory") kind. That is a puzzle: direct realism about inner "voices"! To the wider question, though, it is helpful to...

There are objective scientific tests which show that we don't all see colours the same, such as the Ishihara test for colour vision. Most people don't even see the same "colours" out of both eyes. For many people the left eye might see things more saturated than the right. The question should also perhaps be refined a bit. Shouldn't it be formulated as whether we see things (objects, surfaces, volumes etc.) in the same colours? "Do we see colours the same?" as it stands seems to mean, "Do you see red as I see red?" But this presupposes that we are both seeing red, and then the question seems to ask whether we see it the same way, for example with the same degree of saturation or exactly as blue.