Second-order perception and the knowledge argument

Here’s something odd in the knowledge argument as usually formulated. According to the knowledge argument, Mary who was raised in a black and white argument but knew all of science came to know what it is like to see red by seeing red, despite having known all the physical facts first.

But note that one cannot simply come to know what it is like to see red by seeing red. One knows what it is like to see red by having the second-order perception of oneself seeing red. When one has the first-order perception without the second-order one, one doesn’t directly know that one has the first-order perception. (One may be able to infer it, of course: Here is a tomato, my eyes are open and are pointed towards it, so I am seeing it.) Of course, typically when one has the first-order perception, one also has the second-order perception (but typically not the third-order one), but the point remains is that it is not by the first-order perception, but by the second-order one, that one learns what it is like to see red.

Presumably, any ordinary human perception can be mistaken: it can occur in the absence of its object. Thus it is possible to have the second-order perception without the first-order one. It follows that it is possible for Mary to know what it is like to see red without ever seeing red: all she needs is the second-order perception.

This does not seem to me to damage the knowledge argument as such, but merely to tweak it. For even after the above reflection, it still seems plausible that one doesn’t know what it is like to see red on the basis of physical facts, but by means of a second-order perception. Moreover, we now have an answer to the memory objection to the knowledge argument, namely that just as you and I can know what it is like to see red by having true memories of seeing red, so too someone could know what it is like to see red by having false memories of seeing red, and so actual perception of red is not needed. But this does not affect the argument once we have realized it’s about the second-order perception. For memories, true or false, of seeing red are a kind of temporally backwards second-order perception.