Agnosticism and Skepticism
Consider a tribe of natural-born agnostics concerning the existence of the external world. This tribe regards it as plain common sense that they do not know whether there are any external objects. They have no inclination to believe in external objects, but neither do they disbelieve in them—they are comfortably neutral on the question. (We may also suppose them to be agnostic on other matters too: other minds, the future, the past, whether there are any gods). They agree that it is possible that external objects exist, but they have no positive tendency to believe in them. At the same time they are not agnostic about the existence of their own minds: they are firmly convinced that they have minds and they take themselves to know many truths about their minds. They are not dogmatic agnostics! We can suppose that the tribe takes up a whole planet populated by (say) 6 billion people; there are no other tribes on the planet that accept the existence of an external world. Agnosticism is simply taken for granted, not disputed, universally shared. If you ask them about their state of knowledge, they will tell you that they are certain that agnosticism is the right position; nothing else is rational. They will point out that they are not agnostic about their own mental states, because these are directly given to them, and then note that no such direct knowledge is possible for the material world (if there is such a thing). Confronted with our habitual beliefs about the external world, they would declare us credulous epistemic dupes. These folks are cautious to the marrow.
What do the philosophers of this tribe do with their time? They are certainly not skeptics like our skeptics: there are no positive beliefs held by their compatriots about the external world that they can deem unwarranted. They are not skeptical about widely held beliefs of this type, since there are no such beliefs to be skeptical about. No one believes in an external world, so there is no need to urge epistemic caution with respect to such beliefs. There is no point in philosophy classes that set out to disabuse the young of the dogma of the external world, because no one accepts that dogma—it would be like taking coals to Newcastle. So are the epistemologists out of business on the agnostic planet? Is there nothing they can disagree with? Is there no demand for their services? Like philosophers everywhere, they take it as their duty to question widely held beliefs, but the beliefs that exist on their planet are not like the beliefs that exist on our planet. Still, some beliefs exist there—so there is something to question. What might they fasten on?
I envisage two lines of questioning that might occur to them: first, questioning people’s confidence in their judgments about their own minds; second, questioning people’s confidence that agnosticism about the external world is the only reasonable position. There might be professional epistemologists on this planet whose reputations are built around these two lines of questioning. The universal agnostics will wonder why people subscribe to such a sharp contrast between the mind and the external world, pointing to cases in which (they claim) people make mistakes about their own minds. Thus we have skeptics with respect to knowledge of the internal world—they are skeptical of the generally held belief that knowledge is possible here. Then we have those philosophers skeptical of agnosticism about the external world: they question the belief that the external world cannot be known. In the culture of the tribe this kind of philosopher is deemed the more radical: for in that culture agnosticism about the external world is so deeply entrenched that any attempt to question it is immediately suspect. At least the first kind of philosopher doesn’t attack the very roots of their belief system; she merely suggests extending their general agnosticism all the way down. That seems to them epistemologically commendable: it is good not to overreach in matters of knowledge attribution, and it is salutary to be reminded that even in the securest of domains there is always room for doubt. These skeptics have their heart in the right place, merely preaching a general caution that is taken as gospel elsewhere. Their motto is: It’s always better to be cautious than wrong.
But those who suggest that agnosticism about the external world is a false doctrine are another kettle of fish: for they are claiming to have knowledge that it is manifestly impossible to have. Everyone agrees (save the odd madman) that no one can know that external objects exist–no matter how much it may seem that they do (and things don’t really seem that way to deep-dyed agnostics); and yet these so-called “philosophers” keep insisting that they can and do know that. This strikes ordinary hardworking people as a laughable conceit, wildly counterintuitive on its face, and vaguely unethical to boot. It therefore provides good material for radical professors giving university classes to susceptible young minds. Government officials regularly complain that professors are trying to convince the young that they can know that they have a body. Outrageous! Any fool can see that such knowledge is impossible; to suggest otherwise is to undermine the very fabric of civilization—built as it is on the incontrovertible principle that it is wrong to believe that which cannot be proven. To claim knowledge of an external world is to fly in the face of centuries of hallowed tradition, as well as conflicting with the innate Light of Reason. But those wayward philosophers stubbornly maintain that they have arguments for their subversive views, paradoxical as their arguments may sound. Some claim that external objects are really constructions from sense data, and we can know of their existence. Others hold that inference to the best explanation justifies belief in an external world. Yet others maintain that they know intuitively that external objects exist, or that God has disclosed this fact to a select few. Interestingly, no one is ever persuaded by these arguments, except in a feebly academic sense. They may accept the existence of an external world while closeted in the study, but when they return to ordinary life they slip back into their habitual agnosticism (and in truth the philosophical arguments are just not very good). It is just so much more natural to believe that human knowledge is limited, and that nothing can be inferred from the existence of an inner world about the existence of an outer world. The philosophical arguments may be ingenious and fun to think about, but they do nothing to dislodge the deep-seated agnosticism of our tribe. Their natural caution is not so easily shattered.
The lesson is that philosophical skepticism exists against a cultural (or biological) background of generally held assumptions—it is skepticism with respect to a particular body of entrenched beliefs. In our case the body of beliefs entails that there is an external world and that it has a certain character—we take ourselves to know things about this world. The skeptic questions our general confidence in these beliefs. In the case of the agnostic tribe the body of beliefs entails that nothing can be known about an external world—and that this fact can itself be known. The skeptic then questions this assumption, holding that the external world can be known to exist. This is equally a form of skepticism, since it questions a widely held belief—it is skeptical with respect to that belief. There is no such thing as skepticism tout court—as if the only conceivable kind of skepticism questions the belief that certain things can be known. Some skepticism questions the belief that certain things can’t be known. It all depends on the culture in which the skeptic operates. If a culture believes that the existence of the gods can be known, but not the existence of the self, then skepticism will take a very different form in that culture. The skeptic here would claim that the existence of the gods cannot be known, but the existence of the self can be. Someone who denies that the existence of external objects can be known is not ipso facto a skeptic—since no one may contest that claim. The skeptical philosophers on the agnostic planet defend knowledge of the existence of the external world, but they are nevertheless skeptics—relative to that culture. The naturally agnostic people are not skeptics, because they challenge no generally accepted beliefs. It never even occurs to them to believe in external objects, so their agnosticism is not a rejection of anything believed. Agnosticism is not in itself a form of skepticism—it merely asserts that certain things can’t be known.  To be a skeptic you have to challenge something that is generally believed, but what is believed can vary from case to case. Skepticism is culturally relative: to be skeptical is to be skeptical with respect to the beliefs of a culture. Skepticism is essentially an attack on entrenched beliefs, not a set of beliefs in its own right. This is why epistemic caution can be an object of skepticism, as well as epistemic recklessness.
 If you say that we can’t know about galaxies beyond the reach of light or exactly how many dinosaurs there were, you are not a skeptic—since no one disagrees with you. A skeptic needs an opponent, preferably a large group of them.