In the eighteenth century, the Scottish philosopher David Hume wrote that human reason is “the slave of the passions.” If Hume had meant by “passions” what we mean by that word today, his observation wouldn’t be worth noting. Obviously, when we’re seized by intense feelings like lust or vengeance, our reasoning faculties are not running the show. But Hume meant “passions” in a different sense; he meant feelings, broadly speaking. He was saying that, though rational thought plays an important role in human motivation, it is in a certain sense never really calling the shots. When we decide to do something, we decide on the basis of a feeling.
Where did Hume get this idea? Apparently through introspection—carefully watching his mind at work. In a sense, Hume was being mindful before mindfulness was cool. Indeed, as Western philosophers go, Hume was pretty Eastern. A number of his views align almost uncannily with Buddhist thought, including an argument he mounted against the existence of the self. Some scholars have suggested that this may be no coincidence, that he may have somehow encountered Buddhist ideas even though they had barely begun to drift westward from Asia. Certainly the idea that feelings run more of the show than we realize is Buddhist in spirit.
Now, a quarter of a millennium after Hume caught up with Buddhism, science is catching up with Hume. It has developed tools to peer into our motivational machinery, to see which parts of the brain are active when we make decisions. And Hume’s ideas about the relationship of reason to feeling, long considered radical, are looking pretty good.
Consider a decision as straightforward as whether to buy something. It’s tempting to think of this as an exercise in rational deliberation. You look at the product and the price, and then you ask yourself a series of questions: How much would you use the product? Would the purchase take a big chunk of your cash? What else could you buy with that money? After answering such questions, you coolly weigh the factors for and against the purchase and decide.
But weighing factors may not be so cool after all, according to an experiment done by cognitive scientists at Stanford, Carnegie Mellon, and MIT. They gave people real money and offered them a series of things to buy: wireless headphones, an electric toothbrush, a Star Wars DVD, and so on. As these people were shown each product, and then its price, their brains were being scanned. It turned out researchers could do a good job of predicting whether someone would purchase something by watching which parts of the brain got more active and which got less active. And none of these were parts of the brain mainly associated with rational deliberation; rather, they were parts associated with feelings. Like, for example, the nucleus accumbens, which plays a role in doling out pleasure and gets more active when people anticipate rewards or see things they like. The more active the nucleus accumbens while subjects were looking at a product, the more likely they were to buy it. On the other hand, there’s the insula, which gets especially active when people anticipate pain and other unpleasant things. The more active the insula got when people were shown the price, the less likely they were to buy the product.
Though weighing the pros and cons of a purchase sounds like a purely rational, even mechanical act, this experiment suggests that the way the brain actually does the weighing is through a contest of conflicting feelings. Even the factor of price—a purely quantitative index, the kind of thing that is easily fed into a computer’s decision-making algorithm—ultimately enters the equation in the form of a feeling, a degree of aversion. And the stronger feeling—attraction or aversion—wins.
To be sure, these feelings may be informed by reason. If you remind yourself that the last electric toothbrush you bought went unused and infer that this is the likely fate of your next electric toothbrush, any feeling of attraction to the toothbrush may fade. If you remind yourself that the $20 they’re asking for the toothbrush is less than you spent on dinner last Friday, your aversion to the price—and activity in your insula—may weaken.
Why Feeling Governs Thought
So reason does play a role in what a person finally does. Still, this experiment suggests that maybe reason can play that role only by influencing the ultimate motivator: feelings. As Hume put it, “Reason alone can never be a motive to any action of the will.” Buying something ultimately comes down to feeling good about the purchase—or at least feeling better than walking away from the purchase feels. Of course, you may later regret walking away; “nonbuyer’s remorse” is as real as “buyer’s remorse.” But either way, the key word is remorse. The Monday-morning quarterbacking comes in the form of a feeling because that’s the form the Sunday quarterbacking assumed in the first place….