Chapter 1: Introduction and Overview
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Chapter 1 Introduction and Overview Felix qui potuit rerum cognoscere causas. (Happy is one who could understand the causes of things.) Virgil, Georgics ii.490 Causality plays a central role in the way people structure the world. People constantly seek causal explanations for their observations. Why is my friend depressed? Why won’t that file display properly on my computer? Why are the bees suddenly dying? Philosophers have typically distinguished two notions of causality, which they have called type causality (sometimes called general causality) and actual causality (sometimes called token causality or specific causality; I use the term “actual causality” throughout the book). Type causality is perhaps what scientists are most concerned with. These are general statements , such as “smoking causes lung cancer” and “printing money causes inflation”. By way of contrast, actual causality focuses on particular events: “the fact that David smoked like a chimney for 30 years caused him to get cancer last year”; “the fact that an asteroid struck the Yucatan Peninsula roughly 66 million years ago caused the extinction of the dinosaurs”; “the car’s faulty brakes caused the accident (not the pouring rain or the driver’s drunkenness)”. The reason that scientists are interested in type causality is that a statement of type causality allows them to make predictions: “if you smoke a lot, you will get (or, perhaps better, are likely to get) lung cancer”; “if a government prints $1 billion, they are likely to see 3% inflation”. Because actual causality talks about specific instances, it is less useful for making predictions, although it still may be useful in understanding how we can prevent outcomes similar to that specific instance in the future. We may be interested in knowing that Robert’s sleeping in caused him to miss the appointment, because it suggests that getting him a good alarm clock would be useful. Actual causality is also a critical component of blame and responsibility assignment. That is perhaps why it arises so frequently in the law. In the law, we often know the relevant facts but still need to determine causality. David really did smoke and he really did die of lung cancer; the question is whether David’s smoking was the cause of him dying of lung cancer. Similarly, the car had faulty brakes, it was pouring rain, and the driver was drunk. Were the 1 2 Chapter 1. Introduction and Overview faulty brakes the cause of the accident? Or was it the rain or the driver’s drunkenness? Of course, as the dinosaur-extinction example shows, questions of actual causality can also be of great interest to scientists. And issues of type causality are clearly relevant in the law as well. A jury is hardly likely to award large damages to David’s wife if they do not believe that smoking causes cancer. As these examples show, type causality is typically forward-looking and used for prediction . Actual causality, in contrast, is more often backward-looking. With actual causality, we know the outcome (David died of lung cancer; there was a car accident), and we retrospectively ask why it occurred. Type causality and actual causality are both of great interest and are clearly intertwined; however, as its title suggests, in this book, I focus almost exclusively on actual causality and notions related to it. Most of the book focuses on how to define these notions. What does it mean to say that the faulty brakes were the cause of the accident and not the driver’s drunkenness? What does it mean to say that one voter is more responsible than another for the outcome of an election? Defining causality is surprisingly difficult; there have been many attempts to do so, going back to Aristotle. The goal is to get a definition that matches our natural language usage of the word “causality” (and related words such as “responsibility” and “blame”) and is also useful, so that it can be used, for example, to provide guidance to a jury when deciding a legal case, to help a computer scientist decide which line in a program is the cause of the program crashing, and to help an economist in determining whether instituting an austerity program caused a depression a year later. The modern view of causality arguably dates back to Hume. (For the exact citation, see the notes at the end of this chapter.) Hume wrote: We may define a cause to be an object...


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