Science is the process through which we derive reliable predictive rules through controlled experimentation. That’s the science that gives us airplanes and flu vaccines and the Internet. But what almost everyone means when he or she says “science” is something different. … Since most people think math and lab coats equal science, people call economics a science, even though almost nothing in economics is actually derived from controlled experiments. Then people get angry at economists when they don’t predict impending financial crises, as if having tenure at a university endowed you with magical powers.
One way of systematically understanding the world is just to watch it and write down what happens. “Today I saw this bird eat this fish.” “This year the harvest was destroyed by frost.” “The Mongols conquered the Sung Dynasty.” And so on. All you really need for this is the ability to write things down. This may sound like a weak, inadequate way of understanding the world, but actually it’s incredibly important and powerful, since it allows you to establish precedents. … A second way of systematically understanding the world is repeated observation. This is where you try to make a large number of observations that are in some way similar or the same, and then use statistics to identify relationships between them. … The first big limitation of empirics is omitted variable bias. You can never be sure you haven’t left out something important. The second is the fact that you’re always measuring correlation, but without a natural experiment, you can’t isolate causation. Still, correlation is an incredibly powerful and important thing to know. … Experiments are just like empirics, except you try to control the observational environment in order to eliminate omitted variables and isolate causality. You don’t always succeed, of course. And even when you do succeed, you may lose external validity – in other words, your experiment might find a causal mechanism that always works in the lab, but is just not that important in the real world.
Mankind are so much the same, in all times and places, that history informs us of nothing new or strange in this particular. Its chief use is only to discover the constant and universal principles of human nature, by showing men in all varieties of circumstances and situations, and furnishing us with materials from which we may form our observations and become acquainted with the regular springs of human action and behaviour. These records of wars, intrigues, factions, and revolutions, are so many collections of experiments, by which the politician or moral philosopher fixes the principles of his science, in the same manner as the physician or natural philosopher becomes acquainted with the nature of plants, minerals, and other external objects, by the experiments which he forms concerning them.