Unconscious thought is an oxymoron. Thought has to spring from consciousness. Random images and sensations arent thoughts. We make thoughts happen. Thoughts dont happen to us.
"But what is it to think?"
To think is to create: connections, solutions, ideas, stories, songs, images, etc. To create requires consciousness.
"But what is it to be conscious?"
To be conscious... to be aware... is to acknowledge that you are, and that the world around you is.
"Still making sense so far. Next question is, how are we sure that we are conscious or that the things that we are aware of are really things and not merely hallucinations which the mind projects into itself?"
It doesnt matter whether what we are aware of are hallucinations or 'real' things. What matters is that we are aware of them, that we are aware we are in them, that we are aware of something. We acknowledge something: us and the 'world' around us. Consciousness does not concern itself with whether the self or world being acknowledged is 'real' or 'illusory'.
We can never be sure there is 'something' out there that gives off characteristics like color and form and smell or whatever. What is a thing apart from its characteristics and properties? Probably an idea of a thing, probably a 'real' thing. Im going with the latter. Not because Im sure, but because it makes more sense to me that there is something out there apart from us, independent of us, that gives off something that we interpret as properties and characteristics because of the way we interact with whatever it is that these things give off. It is possible that we supply these characteristics from the something just because of the way we are built and that the something doesnt really give them off.
"Nice! now, next questions would be, how can we be sure that our consciousness is the same as others'; that we are not alone in our solipsistic view that the self can only affirm these impressions only insofar as they interact with the "itself?" if indeed we are conscious, then how can we be sure that others are indeed conscious as well, and that this consciousness is the same as ours? after all, in affirming that the objects of consciousness could be real or illusory, then it is possible for only the self to exist and create everything else as an illusion. in fact, this is what happens in dreams; only that the impressions are re-produced instead of passing through the senses. however, the mind is capable of reproducing, and creating these impressions. what we see are merely colors and sounds, we then interpret them as voices, words, pictures, or faces. if this can be done by our minds alone, then it would be impossible for us to distinguish fantasy from reality. all consciousness would be self-consciousness. but this leads us back to an earlier question: what is consciousness?"
Again there's that word 'sure'. We cannot be absolutely sure. We can only be reasonably sure. Fortunately for us, we get to define what 'reasonable' is. For that we need something like what Karl Popper called a metaphysical research programme. This is something not borne out by evidence but is useful in determining the direction of a scientific research project and in interpreting the data. For example, in this case, we cannot be sure that our consciousness is the same as others so we create a metaphysical research programme that assumes that our consciousness is the same as others. We then conduct experiments: interacting with people, observing them, collecting data, and interpreting results all of this based on the metaphysical research programme. We find that our observations tally with our programme. Our observations do not refute it. Therefore it works; it is useful. For all intents and purposes, it is 'true.'
We can also create another metaphysical research programme that assumes that only we exist and all the rest are illusory. We do the same thing: interacting with people-illusions, observing them, collecting data-illusions, and interpreting results all of this based on the metaphysical research programme. We may also find that our observations can be explained by the programme. It also works and is useful. But it isnt popular. It isnt 'common sense.' So adherents of this view in the real everyday world languish in the loony file for now, probably just biding their time until the idea can make its comeback, comes back to acceptability, and replaces the old programme.
It is much like when the universe revolved around the earth. With this paradigm, astronomers were able to make accurate predictions about stellar and planetary motion, even though they were operating within the wrong premise. Their observations were useful, and therefore at that time, 'true.'
How can we be sure? We can't. We can only go with what works and, to a certain extent, with what is currently acceptable.