Being Wrong - Kathryn Schulz [26]
The fallibility of perception was a thorn in the side of early philosophers, because most of them took the senses to be the main source of our knowledge about the world. This raised an obvious question: if we can’t trust our senses, how can we trust our knowledge? One early and clever solution to this problem was to deny that there was a problem. That was the fix favored by Protagoras, the leader of a group of philosophers known as the Sophists, who held forth in ancient Greece around the fifth century BC. Protagoras agreed that the senses were the source of all knowledge, but he categorically denied that they could be wrong. You might imagine that this conviction would lead to a kind of absolute realism: the world is precisely as we perceive it. But that only works if we all perceive the world exactly the same way. Since we don’t, Protagoras wound up espousing radical relativism instead. To borrow an example from Plato (whose extensive rebuttal of the Sophists is the chief reason we know what they believed): if a breeze is blowing and I think it is balmy and you think it is chilly, then what temperature is it really? Protagoras would say it is warm to me and cold to you, and that’s that. There is no reality “out there” for the senses to perceive or misperceive; the information provided by our senses is reality. And if my senses happen to contradict yours—well, then our realities must differ. In matters of perception, Protagoras argued, everyone was always right.
Protagoras deserves recognition for being the first philosopher in Western history to explicitly address the problem of error, if only by denying its existence. For most of us, though, his position on perception is intrinsically unsatisfying (much as relativism more generally can seem frustratingly flaccid in the face of certain hard truths about the world). Plato, for one, thought it was nonsense. He noted that even a breeze must have its own internal essence, quite apart from whoever it blows on, and essentially advised Protagoras to get a thermometer. But Plato also rejected the whole notion that our senses are the original source of knowledge. Since, as I mentioned earlier, he thought our primordial souls were at one with the universe, he believed that we come to know the basic truths about the world through a form of memory. Other philosophers agreed with Protagoras that the senses are a crucial conduit of information, but, unlike him, they acknowledged that perception can fail. This seems like a reasonable position, and one we are likely to share, but it raises two related and thorny questions. First, how exactly do our senses go about acquiring information about the world? And second, how can we determine when that information is accurate and when it is not?
Early philosophers regarded the first question as, essentially, a spatial-relations problem. The world is outside us; our senses are within us. How, then, do the two come together so that we can know something? Obviously our senses can’t go forth and drag an actual chunk of the world back to their internal lair, intact and as is, for the benefit of the rest of the brain. But—outside of dreams, hallucinations, and madness—most perceptions aren’t produced solely by our minds either. Instead, our senses must somehow bridge the gap I described in Chapter One: the rift between our own minds and everything else. One way to understand how they do this