Thoreau several times asks us to look in a pool of water and catch an intermixing of realities that are usually taken to be oppositional. Look into a puddle and see both the muddy bottom and the sky above. Heaven and mud are usually conceived as infinitely different. But the eye now takes in both heaven and mud, stars and pebbles, simultaneously. Thoreau calls this a ‘double intention’ of the eye. You know these are separate intentions because you can deliberately cancel out layers — attend only to the pebbles, and stars disappear; attend only to stars, and pebbles disappear.
You could take Thoreau to be reversing the thrust of the classic “argument from illusion” that has us look into a reflection and know that since we can’t grab the stars with the hand that grabs the pebbles, we don’t really see stars amidst pebbles — therefore the senses deceive. But Thoreau counters that since we DO see stars and pebbles mixed, therefore the senses can deliver more than we might think possible. Reality is thereby augmented rather than deflated.
Lucretius has obviously been reading Thoreau and writes [in book four of “The Nature of Things] “A puddle of water no deeper than a single finger-breadth, which lies between the stones on a paved street, offers us a view beneath the earth to a depth as vast as the high gaping mouth (hiatus) of heaven stretches above the earth, so that you seem to look down on the clouds and the heaven, and you discern bodies hidden in the sky beneath the earth, marvellously” (mirande). (I thanks my friend from Cambridge for supplying this.)
Now I’m happy to have stars cohabiting with pebbles and to argue that there’s no illusion here at all. If I foolishly listen to a deflating skeptic who challenges me, saying ‘Well, you know, you aren’t really seeing the heavens in the puddle – you’d have to look up for that” then it’s not hard to isolate the error in the challenge. The skeptic can’t think I don’t know that when my finger jabs into the water it won’t keep extending all the way to heaven. Of course, I know my finger will hit bottom. So the skeptic has no case to make. If I jab at my image in a mirror and stub it on glass, does that prove I don’t really see myself in the mirror? I see myself, not an illusion, and I see the stars in the puddle, not an illusion. Only a very young child or cat would get confused here, and register that confusion by trying to peak behind the mirror, or by trying to pick up stars as well as pebbles from the puddle.
Here it’s the skeptic who needs instruction. He (or she) is interrupting and trashing my perceptions without cause. We might also imagine a skeptic who pretentiously informed me, “you’re not really seeing water, you’re seeing H2O” or “you’re really not seeing stars, you’re only having your retina bombarded by atoms.” Thoreau wants to preserve an abundant reality, one that includes the wonder or marvel of stars beside pebbles and pebbles beside stars, and a heaven cohabiting with mud. He’s right, the eye has several intentions, and reality has several layers, and they can intermix, marvelously.