Ex-Hume-Ing the Truth
For all their differences, Descartes, Locke and Berkeley share one trait: they believe that it is possible to develop an argument that defeats skepticism and gives human knowledge a foundation of certainty. That optimism is not universal among philosophers, as David Hume makes clear in Enquiry Concerning Human Understanding. Hume is probably the most noted of the British empiricists, philosophers who (like Locke and Berkeley) believe that our knowledge comes primarily through our observation of the world around us and not from any inherent set of ideas or rational arguments. Where Hume differs from his fellows is in the amount of faith he’s willing to put into those empirical observations.
He begins by dividing human knowledge into two categories: relations of ideas and matters of fact. Relations of ideas are those claims which are based on human-developed concepts and procedures; they are those situations in which, once you define things in a certain way, certain other things must inevitably result. Once human beings define a square for themselves as a closed figure consisting of two parallel sets of line segment that are perpendicular to each other, and a circle as a closed figure all of whose points are equidistant from some given center point, it becomes impossible to conceive of a figure that is both a square and a circle. The definitions are exclusive; meeting one set of criteria involves not meeting the other. The statement “No square is also a circle” has to be true, given the definitions of square and circle, because to try to imagine its opposite results in a contradiction. In the words of a genius next to whom Aristotle, Plato and Socrates are morons — it’s inconceivable. So is a scenario in which two and two actually does equal five. So, Hume says, as long as we’re calling the shots by defining the terms and concepts being compared, we can achieve certainty in our conclusions.
Unfortunately, there is much in the world that exists independently of human conceptualizing, including a lot of human activity; we may give names to external objects like rocks and trees, but we do not entirely create their nature in the way we define circles into existence. Conclusions about these objects and events are matters of fact. “The moon will be full tomorrow,” “You’ll get sunburn if you stay out in the sun too long,” and “The Phillies will find a way to lose crucial games in the second half” all fall into this category. What differentiates matters of fact from relations of ideas is that imagining the opposite of a matter of fact doesn’t result in an inconceivable contradiction. I can imagine tomorrow night being a new moon, or being out in the sun without getting sunburn, or even the Phillies not choking during the stretch run. So no matter how unlikely the opposite of a matter of fact may be, there’s no rational reason to pronounce it impossible. Without such a reason, there is no way that our conclusions on matters of fact can be grounded in absolute certainty. Despite the protestations of other philosophers, skepticism is still in the game.
Furthermore, Hume asks, what is the basis for any of our faith in our conclusions regarding mattes of fact? He argues that this faith is grounded in our reliance on prior experience, in a belief that the future will continue to resemble the past. The sun rose in the east yesterday, the day before, and all the days before; it’ll rise in the east tomorrow. I threw a hundred rocks out my window (very small rocks) and they all fell to the ground; so will the hundred and first. That belief, in turn, is grounded in our belief in the principle of cause and effect, that any set of events can be traced back to some other set of events and– this is important– that the principles along which these events can be tied together are constant. If I get a letter postmarked from London from a friend of mine, I assume that my friend was in London around the time that the letter was sent, because I trace the effect of a postmarked letter to the cause of a postmarking person in London. If letters had a habit of just randomly materializing in my house, or if post offices used any old city name in assigning postmarks, then I couldn’t have faith in the causal chain, and so I couldn’t have much faith in my ultimate conclusion.
Ah, but why do we believe in the principle of cause and effect? At any given moment, without any recourse to what has gone on before, is there anything in the current set of circumstances that suggests that a certain result is the inevitable outcome? Hume uses the example of pool; if you have never seen a game of pool, have never seen spheres knock into each other, and have never studied the laws of motion, is there anything about the mere rolling of a ball toward another ball that suggests what will happen next? No, there isn’t. If I toss that hundred and first rock out the window, there’s nothing about the rock itself that suggests that it’s going to move downward; I can just as easily imagine it falling up. And I can’t bring any of my prior experience into account, Hume says, because the entire question is whether cause-and-effect provides a rational justification to use prior experience to form conclusions. If I say I believe that the future will resemble the past because of cause and effect, and then I say that I believe in cause and effect because I expect the future to resemble the past, I’m just going round in circles.
The answer, according to Hume, is to stop asking rationality to do all the work. Human beings have an ingrained capacity to form habits; when they do or see the same thing over and over again, it forms a kind of groove in their thinking. These grooves can’t be rationally proven or established, so skepticism will never be defeated by a purely rational argument. But the habits we form — like believing in cause and effect, or relying on past experience — do help us navigate the world more or less successfully. We have to keep an eye on them, and they’re not always perfect. But since the limits of rationality suggest that perfect isn’t possible, it’s worth going with what works — so long as we don’t come to put more faith in our habits than they deserve.
About Dave Thomer
Born and raised in Philadelphia. Studied philosophy at Fordham University in the Bronx, where I made many great friends and met my wonderful wife. We moved back to Philadelphia, where I studied philosophy some more and became a teacher. Online and off, I'm looking for ways that we can be better citizens and build stronger communities.