Other people are a great source of information, and in this unit we’ve looked at some of the ways other people and their beliefs can serve as evidence. The largest single influence other people have on us is through what they tell us. As we’ve seen, we learn a great deal about the world through testimony in one form or another. Learning through testimony requires trust however, and other people are not always trustworthy. We looked at some of the factors that can undermine a person’s credibility, and what we can (and cannot) legitimately infer about a person’s testimony on the basis of other things we know about them. In addition, other people can serve is a good guide for whether our own beliefs are correct. The fact that somebody agrees with us can justly bolster our confidence in its truth, while disagreement can signal that we’ve missed something and should lower our confidence. Last, we looked at what we can infer from the fact that many people believe or like something. As we saw, popularity is not always an indication of truth or of merit.
Questions to ask of Testimony:
- Is the source credible? (history of lying? something to gain? capability/expertise?)
- Is the claim plausible given what you know about the world?
Questions to ask of Negative Ad Hominems:
- Does the feature give reason to suspect that the source is not being honest or sincere in this case?
- Does the feature give reason to suspect that the source is not in a good position to know in this case?
A Question to Ask about Cases of Agreement and Disagreement:
- Is the other person credible about this specific claim?
Questions to ask of Appeals to Popularity
- Are there other plausible explanations for the subject’s popularity?
- Would the truth of the proposed explanation be less surprising than the truth of any competitor?
- The Credibility Assumption
- History of Lying or Deception
- Internet as Testimony Machine
- Ad hominem Argument
- Positive/Negative ad hominem
- Cooperative Disagreement
- Agreement/Disagreement as Evidence
- Appeal to Popularity
- False Consensus
In recent years there has been a dramatic increase in research in psychology and philosophy on testimony. If you are interested in the most recent psychology literature a good place to start is with the overview in “Cognitive Foundations of Learning from Testimony” by Harris et al. in Annual Review of Psychology (2018). For the philosophical point of view see Testimony: A Philosophical Introduction by Joseph Shieber. For more on relationships between testimony, the web, and social media see The Internet of Us by Michael Lynch. Finally, for an excellent introduction to disagreement as evidence, see the aptly titled Disagreement by Bryan Frances.