Let's say I have a two room apartment, and you happen to know everything about the one room and nothing about the other. Then, I submit, you cannot deduce anything about the other room, from known facts about the first one. Getting to the point, I will never discover anything about you only on the basis of my observations on myself, and conversely.
Actually, as someone pointed out, even our own existence is an hypothesis. We don't get to deduce much from nothing, and it would seem foolishly ungenerous not to assume the existence of others also. Then we are in business, the operative word being WE.
Another thing to keep in mind is that we don't start out in life totally assured of our own existence and absolutely ignorant about anything else (Descartes seems to be presupposing something on this order). Rather our own existence as individuals is secondary to the mysterious mother/child-unity, psychologically as much as physiologically.
It is true that I have a kind of privileged access to my own consciousness, but if we look at that carefully, specifically paying attention to the CONTENT of our consciousness, our property rights appear much less obvious. Perhaps I am conscious of you, so that the content of my consciousness is/are you... Then to what, exactly, is it that I have unique access?
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