Modern Philosophy, Winter 2011
According to David Hume, we can draw no firm conclusions about the nature of causation. Instead, we infer that one event causes another because the two events are constantly conjoined in our experience. However, to assume that one event causes another because the two are constantly conjoined in our experience is to commit a fallacy; correlation does not constitute causation. We have absolutely no basis for making claims about how events will affect one another in the future. One could say that our assumptions about the future have always worked in the past, but that is still not a statement about the future—it is a statement about the past. The future is unknowable, and it is impossible to posit causation for any event in our experience.
Suppose that I drop a rock into water and it sinks. Because of my past experience and my knowledge of science, I will assume that the rock sinks because of its weight, volume, and density. But this is not the only explanation. Perhaps the rock is sentient, and upon contact with water it wants to sink, and therefore makes the choice to do so. Perhaps the water itself is pulling and pushing on the rock, forcing it to sink. Or perhaps it sinks because God is controlling everything in the world and is causing the rock to sink [this is the Occasionalist philosophy of cosmology].
Furthermore, the mere fact that the rock I threw into the water a moment ago sank is no reason to assume that the next rock I throw into the water will, in fact, sink. Certainly every rock I have thrown into the water in the past has sunk, but this does not mean that the next one will. Perhaps it will float instead, or perhaps it will bounce off the water and float towards the heavens. In short, I have absolutely no knowledge of what the rock will do in the future until it has actually done it, in which case my knowledge is still not of the future, but of the past.
According to Hume, all of our assumptions about the world are not based on fact, but on habit and custom. Having observed events happening in a certain way, we assume that they always happen that way. For example, many years ago it was thought that all swans were white. Later black swans were discovered to exist in Australia. Obviously, our perceptions of the nature of reality can be flawed and mistaken, and are therefore not to be trusted. And the events inside our minds are no exception. My fingers move on my keyboard because I will them to—or do they? Is it not possible that my fingers are being moved by some other force, and that I only think that it is my will that moves them? Simply because my willing my fingers to move has, in the past, always resulted in them doing so is no reason to assume that the willing is what causes the motion. Our perceptions of causation are the result of what Hume calls “matters of fact”—synthetic a posteriori, or empirical, knowledge. Our knowledge of the past comes only after the past has happened. But this does not entitle us to infer synthetic a priori statements from a posteriori statements. We can only know things about what has passed. We cannot know anything about what is to come.
How does this affect how we are to operate in our daily lives? Obviously, we do not register surprise when objects behave as they always have in the past, because we expect them to behave as they always have as a result of our custom and habit. Hume's view is simply that if we are to be honest with ourselves, we must recognize that we cannot, in fact, make certain predictions about the future, but can only make statements about our past experience.
