Whenever a person chooses a side in the traditional debate between rationalism and empiricism, that person is necessarily making a statement about how much people should trust the evidence of their own senses. However, there are a number of instances in which I think that sensory evidence can be deceptive. While I think the allure of empiricism is undoubtedly seductive, for the precise reason that sensory experience can be so vivid, I think this is a limited worldview. I would like to advance my own preference for rationalism by looking at two basic objections to empiricism -- the presence of innate knowledge in the mind, and the potentially deceptive nature of the senses. The former, I hope, will show that rational processes and structures to a certain degree exist without need of sensory evidence -- that reason and logic are, to some extent, a thing apart from perception. The latter will call into question whether knowledge obtained through the senses is invariably or necessarily knowledge: the presence of all kinds of quirks of perception (from optical illusion to hallucination) suggests that an overwhelming faith in sensory evidence is unwise.
The first point that I would like to make against empiricism entails the presence of intellectual material that is seemingly hard-wired into the brain and thus clearly stands outside of mere sensory experience. This is an argument that was made by Socrates in Plato's dialogue Meno, although the Socratic argument is designed to support a philosophy of knowledge -- in which knowledge is constituted as a form of "unforgetting" or anamnesis -- that I do not think it necessary to endorse in order to make use of Socrates' premises. Socrates in the Meno takes an uneducated slave-boy and uses him to demonstrate that, without any prior mathematical education, the boy can arrive at a fairly advanced geometrical proof simply by following the inherent logic. Although Socrates' ultimate conclusion in the argument -- that the boy is actually remembering knowledge that was possessed in a previous lifetime -- it is not necessary to accept this conclusion in order to understand the revolutionary potential of the argument here. The Socratic emphasis on "this knowledge which he now has must he not either have acquired or always possessed" is an indication of the depth of rational thought (Plato 2008). The "previous lifetime" is actually probably the inherent structure of the brain: systems of pattern recognition and rational thought that do not rely on knowledge obtained through the senses.
I think that personally the better example for this is not the famous Socratic use of geometry, but the much more recent (if equally revolutionary) example of Noam Chomsky's linguistics. The most engaging immediate example I can think of is the rule referred to by linguists as the "expletive infix." Without knowing this descriptive terminology for the phenomenon, most people are familiar with what it is -- it is the insertion of an expletive (or swear-word) into another larger word for rhetorical effect. Familiar examples would include "abso-bloody-lutely" in England, or "in-fucking-credible" in America. However, what linguists who have followed Chomsky's lead have discovered is that we can ask a person: the position where the expletive falls when inserted follows a set of clear rules. If an English speaker is given a word -- "Monongahela," for example -- he or she will automatically know where to place the expletive ("Mononga-fuckin-hela") despite the fact that this grammatical rule has never been taught. Indeed, the rule itself has certain ambiguities, so that some words -- "anticipatory" -- will produce the same double response in all English speakers (who will recognize that, according to a rule they have never been taught, both "an-fuckin-ticipatory" and "anticipa-fuckin-tory" each have some instinctive attraction).
Why is this important? Because it demonstrates profound evidence that argues for the rationalist rather than empiricist position. The presence of such observable quantifiable logical rules -- which somehow are available in the mind of an English-language speaker, despite the fact that these rules have never been taught -- indicates some kind of fundamentally rational structure in the brain which has nothing to do with sensory evidence. Indeed, very few people have ever heard the word "Mononga-fuckin-hela" spoken (outside of Pittsburgh, anyway) so it is impossible that these rules would have been absorbed, learned, or otherwise integrated through sensory perception. But the expletive infix is just one small portion of the larger point about language that has been made by Chomsky -- namely that anyone who speaks English somehow has the ability to create a seemingly infinite number of sentences which he or she has never heard spoken. It would seem that language falls down solidly on the rationalist rather than empiricist side of this debate.
The heavy emphasis placed by empiricism on sensory evidence, however, has an additional problem -- do empiricists not consider that sensory evidence might be deceptive? In advancing this point, I must (like an empiricist) have recourse to an anecdote. I happened to have an acquaintance several years ago who had come out as "transgender" in middle school, and was being given medical injections of testosterone so that he could approximate physically the gender he perceived himself to be. The difficulty was that this person then began to talk with his acquaintances about other symptoms -- describing himself as going blind. However, in talking extensively online about his encroaching blindness, this person would frequently make reference to shared history and contradict things that all his friends knew to be true -- backdating the onset of his supposed blindness to earlier times at which he had never mentioned or exhibited this supposed malady. The simple fact is that I thought he was either hatching a gigantic practical joke or trying to come up with an excuse to legally take his dog to Starbucks with him. I would eventually stop having conversations with this person, but a recent Google search revealed that he now blogs about being in a wheelchair from some mysterious (and never fully articulated) wasting disease. According to the blog, he has had his dog designated as a helper-animal and indeed can take this dog into Starbucks now. But I am left with some pretty troubled questions about this whole process. The medical establishment permits a transgender person to receive treatment for his or her condition more or less by announcing it -- the mere statement in a psychiatrist's office that you believe yourself to be a man trapped in a woman's body is enough to get a prescription for testosterone injections. In some sense, this follows the classical philosophical "problem of other minds" -- what reason would somebody have for claiming to be trapped in a body of the wrong gender unless they really felt that way? But the difficulty comes when we try to distinguish this phenomenon (which is apparently real and leads to a lot of social stigma and ill-treatment) from the further behavior exhibited by the transgender person who was my acquaintance -- the further behavior is clearly what would be described as "factitious disorder," or basically pretending to have a medical condition that you do not. Certainly the person in question exhibited the primary symptom of this mental illness, which is a "dramatic but inconsistent medical history" (Hamilton, Feldman et al., 27) I left communicating with this person feeling so troubled because the simple fact is that I knew this person was lying about being blind. And indeed this person seems to have replaced his friend base, and replaced his factitious illness: he is no longer suffering from rapidly encroaching blindness but is instead blogging about life in a wheelchair. There may be an impossibility of knowing other minds, but there is also no reason to be persuaded by someone's own account of their sensory experience if…