5.1: Other People as Sources of Information

In this chapter, we will focus on other people as sources of information. People’s claims are sometimes called testimony, but don’t let this word mislead you. We will use it to cover any information (and misinformation) we acquire from other people. In this sense, testimony includes the things we hear directly from others, read in newspapers or books, see on television, find on websites, and so on. Think about how much of your knowledge is acquired from others. Your friends tell you about things they have seen or heard. You learn new things when you read the morning paper or a chapter in a textbook or an email message from someone far away. You acquire information when you watch the news or surf the net.

A large society like ours consists of a vast social network in which everyone relies on others for information, and written records and oral traditions extend this network back into the past. If you suddenly forgot all the things you learned from others, there wouldn’t be much left. You wouldn’t even have a language in which you could ask yourself how much you knew. In today’s rapidly changing world, much of what you learn in college will become outdated rather quickly. Hence, it is important for you to learn how to acquire and evaluate information.

Information: We Need Something to Reason About

Testimony bears on reasoning for two closely related reasons.

1. The premises of our reasoning are very often based on things we learn from others.
2. We frequently need background information to know whether the premises of an argument are plausible or whether they omit relevant information, and often we must rely on others to supply this information.

Our premises are often based on the claims of others. Many of our arguments rely on premises that we get from others. To create jobs, suppose your City Council proposes that a nuclear power plant or a toxic waste dump be built near your community. Most of us would care enough to argue for our position on this issue. But we would have to rely on the claims of experts about the risks and reliability of such facilities to support our conclusions about whether a potentially dangerous plant should be built.

Evaluation of arguments often requires background knowledge obtained from testimony. There are three critical questions to ask about any argument we encounter. Do its premises support its conclusion? Are its premises plausible? Has any relevant information been omitted? Often, we cannot answer the last two questions without having a good deal of background knowledge, and frequently we must rely on other people to supply it.

Here’s an example of an issue you could face as a parent. The average child will see over 8,000 depictions of murders on television before they graduate from grade school. Suppose your neighbor urges you to sell your TV so that your little Wilbur won’t grow up to be an axe murderer. In trying to evaluate the argument that TV violence is dangerous for your children, you need background information about the lasting effects of seeing frequent violence on television. Will seeing violent acts on TV make Wilbur more violent?

Or, suppose someone argues that we should retain capital punishment because it deters murders. Here you need background knowledge to determine if their premise that capital punishment really does deter murders is true. And you also need to know whether they have omitted information; for example, it may seem to deter murders in one state (which they mention), but not in other states (which they don’t).

In a heterogeneous, highly technological society like ours, experts are an especially important source of information. We rely on our dentist when we break a tooth, on the telephone repair-person when our phone goes dead, on ESPN.com for the score from last night’s game, on Consumer Reports for help in buying a used car.

It requires effort to obtain useful information. If we sit around passively and hope that useful information will come our way, we will be in trouble. But effort alone isn’t enough. It is often difficult to distinguish genuine experts from self-styled experts who don’t really know what they are talking about. Furthermore, even genuine experts are sometimes biased, and in many cases the experts disagree with one another. Finally, on some matters there may not be any experts at all. This means that we need techniques for identifying experts, and we also need to know what to do when they can’t be found or when they disagree with each other.

We will begin by examining experts in recognized fields like medicine, law, and professional football. We will then consider several factors that make people appear credible; the goal here will be to discover ways in which people can appear to be experts when they really are not. We will then turn to testimony more generally. We will find that the issues that arise in evaluating the claims of experts resemble those we should use for evaluating any sort of testimony, whether it comes from a top expert in some field or a stranger on the street.