The flip side of an appeal to somebody else credibility are arguments that question that person’s credibility. To see what is fair and what is not you need to consider what is relevant when making an appeal to authority of one kind or another. However I would suggest that three over-arching principles apply:
- Questions of credibility should be avoided whenever possible. Even if the intent is not a personal attack, it is naturally difficult to question the credibility of somebody without it seeming like a personal attack. That is even more so if it is the credibility of the person you are directly addressing. Even so, if somebody says they saw an alien kidnapping a yeti you may have to ask questions…
- Questions of credibility should be targeted and limited in scope. Any challenge should be constrained to the issue at hand whenever possible.
- Questions of credibility should be pertinent. A person maybe a criminal or a murderer or disreputable in some way but a challenge to their credibility should be pertinent to the issue.
- Questions of credibility must themselves be sound and based on evidence and reason.
So what kinds of challenges to a person’s credibility are likely to be pertinent?
- Competence – is the claim being made by somebody with the technical skill to make the claim. If it is a medical claim, is the person a medical practitioner and if so is the claim within their specialism?
- Experience – is the claim being made by somebody with the relevant experience of the situation. If it is cooking advice is it from somebody who does a lot of cooking?
- Reliability – is the person making the claim reliable? Do they have a track record of making claims that are true?
- Honesty – is the person honest or do they instead have a track record of telling untruths?
- Unbiased – is the person making claims on issue in which they could be expected to have an unbiased viewpoint?