This is the second problem: What is the faculty that enables us to escape from the world of appearance presented by our prereflective innate dispositions, into the world of objective reality? And what, besides consciousness, do we have to add to the biological story to make sense of such a faculty? The distinctive thing about reason is that it connects us with the truth directly. Perception connects us with the truth only indirectly. When I see a tree, I see it because it is there, but not just because it is there. Perception is not a form of insight: I do not grasp the presence of the tree immediately, even though it may seem so prior to reflection. Rather I am aware of it because the tree causes a mental effect in me in virtue of the character of my visual system, which we may suppose has been shaped by natural selection to react in this way to light reflected from physical objects. Having such a system, together with other perceptual and motivational dispositions, enables me to survive in the world. So it is only in a complicated and indirect sense that when I see a tree, I see[…]
Thomas Nagel from “Mind and Cosmos”