It does not seem self-evident to me that the present surface content of our own minds are more reliably known than external objects. In fact, it is by these external objects that we confirm that our senses are reliable. If our minds had no external objects to perceive, we would never develop surface thoughts at all. If you were born as a brain in a vat for example, having grown up as a brain in a vat, not in a mother's womb, I suppose you wouldn't have any thoughts at all, or if you did they would be very much unrecognizable to us. You bring up the example of pain. If I were to experience the pain of breaking my leg but I happened to be dreaming, my brain might send pain signals identical to the signals it would send if I had actually broken my leg. Upon waking and reviewing my leg, any residual pain from the dream would quickly subside, having been corrected by external objects.
It does not seem self-evident to me that the present surface content of our own minds are more reliably known than external objects. In fact, it is by these external objects that we confirm that our senses are reliable. If our minds had no external objects to perceive, we would never develop surface thoughts at all. If you were born as a brain in a vat for example, having grown up as a brain in a vat, not in a mother's womb, I suppose you wouldn't have any thoughts at all, or if you did they would be very much unrecognizable to us. You bring up the example of pain. If I were to experience the pain of breaking my leg but I happened to be dreaming, my brain might send pain signals identical to the signals it would send if I had actually broken my leg. Upon waking and reviewing my leg, any residual pain from the dream would quickly subside, having been corrected by external objects.