Nagel's Argument

We experience consciousness. in that sense it is real
          And so any full account of the world must discuss it
Reductionism cannot violate this condition of realism

You could not explain consciousness away
     In the way that an atheist might explain away belief in god
     Or a psychiatrist belief in witches

Nagel both
1 accepts the possibility that psychology may explain everything
and
2 offers a qualified defense of Cartesianism

Nagel is not making any empirical claims about what science can do
     He is only arguing about how to understand any scientific results.