David Hume

Hume was one smart guy. He started university at 10, and he wrote one of the greatest books of philosophy when he was 26.

His early life, though, seems to have been a bit of a disaster. His father died when David was only two. Nobody liked his first book—the important one—and after he graduated, because he was sick all the time, he couldn’t keep a job.

When Hume applied for the “Chair of Pneumatics and Moral Philosophy” (a job title I would kill for), he was turned down. He applied for another professorship, and was turned down again. Out of desperation, he tutored the Marquess of Annandale—but he turned out to be insane.

Hume then tried to fight against the French in Quebec, but the boats never made it. He tried to fight the French in France, but the raid failed. He went to work as a librarian, but got fired for ordering porn for the library.

While a librarian, though, Hume wrote the book that made him rich, The History of England. Unsurprisingly, he became vastly more popular, and, oddly, especially with the French, who he had only recently tried to kill. Apparently, French women just loved him. He did eventually move home to England, but he never stopped having parties with the young and beautiful.

In his late fifties, he fell in love with Nancy Orde, who was a total fox, smart, and by all accounts a real catch. Orde loved him in return, and they may even have been engaged. Hume died, however, of stomach cancer. By all accounts, he died cheerfully though, as usual.

Hume was the last of the triumvirate of British empiricists. Empiricists believe that we attain knowledge through our senses and by studying the external world.

To us, of course, this seems obvious. Recall, though, Descartes’ belief: the senses are plainly fallible, and it is impossible to build a sound science upon them. In the following selection, Hume builds the argument in reverse: he takes the senses seriously and trusts them. Surprisingly, thoughtful empiricism brings us right back to a point very near skepticism: almost everything is thrown into doubt. And so, despite being separated by a century, a language, and an ideology, Hume and Descartes turn out to have something in common.

Nobody takes Hume’s ideas seriously—not even Hume. To do so is to entirely destroy the idea of science, because Hume destroys empiricism. Like Descartes, Hume asks, “What do you really know?” and it turns out, we don’t know very much at all.

Take two billiard-balls for example. When the first crashes into the second, it sends the other off in a predictable way. But how does it do that? We never actually see the cause; all we ever see is one thing, then another thing. We only assume that we saw the first thing cause the second.

Scientists might say that we generalize from our experiences. But, as an argument, that doesn’t work at all: at best, we would get uncertain generalizations—that bread is usually nutritious, for instance—but if we try to be more certain, we end up making a circular argument:

  1. So far, our generalizations have been trustworthy
  2. Therefore, our generalizations will be trustworthy.

The circularity lies in that tricky transition from premise 1 to 2: we’re making a generalization about generalizations!

This is the “problem of induction”. Induction is, roughly, science. We look at the world and draw generalizations about it. How can we do that when the world changes all the time, and we can’t see deep inside its mysterious workings? An example might help.

Alice and Biljana are in a bar. Biljana’s getting a divorce, and she turns to Alice, her lawyer friend, and says “Alice, I’m really stressed. I don’t know how to find a lawyer I can trust. How can you tell?”

Biljana’s eyes brighten. This is something she knows about. “Alice, it’s easy. You look for a lawyer whose shoes match their bag. It’s that simple! All the best lawyers colour coordinate.”

“Wait, wait! Really? That seems crazy.” Alice says. “How do I know I can trust your advice?”

Biljana replies, “Alice, just look at my shoes and bag! They match!”

Scientists are like lawyers. When they’re asked “How do you know that you can draw conclusions from evidence?”, they reply, “Easy—just look at the evidence! Most times when we draw conclusions from evidence, the conclusion’s correct!”

Like Biljana, they’ve missed the point: drawing a conclusion from evidence about drawing conclusions from evidence is arguing in a circle. The question is “why does induction work?” not “what evidence do we have that induction works?” To answer the second question, you use induction to show that induction works, assuming the very point you’re trying to prove.

So what really do we know? It turns out that empiricism (Hume) and rationalism (Descartes) end up quite close together and show that we know almost nothing at all. Philosophy ends in despair.

It will take Kant, the greatest philosopher in 2000 years, to set philosophy back on its feet.