Philosopher George Berkeley radicalized this mode of inquiry: “When we do our utmost to conceive the existence of external bodies, we are all the while only contemplating our own ideas.” Berkeley’s argument was that we have no experience of material objects that exist outside the perceptual apparatus of our mind and senses. Both the primary and the secondary qualities of objects are perceived in this way. We don’t experience the ocean, we experience only our image and sound and feel of the ocean. Berkeley famously concluded that we have no warrant for believing in a material reality existing independent of our minds!
The great Samuel Johnson famously “refuted” Berkeley by kicking a rock. There! The rock exists! Alas, this is no refutation. Berkeley’s reply to Johnson would be that his entire experience, from perceiving the rock to the sharp pain he felt upon kicking it, occurred entirely within his mind. And Hume completed Berkeley’s skeptical argument by applying it to human beings themselves. We have no experience of ourselves other than our sensations and feelings and thoughts. While we know that sensations and feelings andthoughts exist, we have no basis for postulating some “I” behind them that is supposed to be having those reactions.
It was Hume, Kant wrote, who awakened him from his “dogmatic slumber.” Kant conceded Berkeley’s and Hume’s point that it is simply irrational to presume that our experience of reality corresponds to reality itself. There are things in themselves—what Kant called the noumenon —and of them we can know nothing. What we can know is our experience of those things, what Kant called the phenomenon. If you have a dog at home, you know what it is like to see, hear, smell, and pet it. This is your phenomenal experience of the dog. But what is it like to be a dog? We human beings will never know. The dog as a thing in itself is hermetically concealed from us. Thus from Kant we have the astounding realization that human knowledge is limited not merely by how much reality there is out there, but also by the limited sensory apparatus of perception we bring to that reality.
