Problem
A. Descartes claims that he "regularly has all the same experiences while asleep as madmen do when awake." Suppose your dreams aren't quite as vivid as Descartes's: you only dream in faint shades of gray, and you only dream about dragons. Does that mean that you should not be worried by the thought that you don't know you are not dreaming?
B. There is arguably a disanalogy between Jonathan Vogel's example of Dr. G and ordinary cases of knowledge by perception, say, knowing that there is a book on the table in virtue of seeing a book on the table. Suppose Dr. G knows that Roger has an allergy because this hypothesis best explains Roger's symptoms. Dr. G's knowledge involves fairly sophisticated reasoning from her evidence that Roger is sneezing, that Roger has moist eyes, and so forth. If knowing my vision that there is a book on the table is similar, presumably, it also involves sophisticated reasoning. Is this plausible? How do you think Vogel would respond to this worry?