1. Critical Thinking Lecture 6 Judging Credibility
By David Kelsey

2. Credibility To be credible is to be believable.
It is to be worthy of believing in or about.
Both claims and sources can be credible.
Credibility from reasons: Thus, the credibility of a claim or source comes from the justification or reasons we have for believing that claim or source.

3. The credibility of claims
Claims have credibility
A claim can lack credibility, for example the claim that some birds can fly up to the moon.
The credibility of a claim comes in degrees
Compare Barack Obama sends weekly bribes to the Supreme Court to Barack Obama is a space alien

4. Inherent Credibility
It is reasonable to be skeptical and suspicious if a claim lacks credibility inherently or comes from a source that lacks credibility.
A claim lacks inherent credibility to the extent that it conflicts with what we have observed or our background information or with other credible claims.
For example if a claim conflicts with something I myself have observed it is best to dismiss it. Say, for example, my friend tells me that the mail isn’t being delivered today but I just saw it delivered…

5. Background Information
A claim should also be dismissed if it conflicts with your background information.
Your background information is the immense body of justified beliefs that you know.
This is everything you have ever learned through your own observations or from others.
We call this information background information because, for any of it, one may not be able to specify where she learned it or who she learned it from.
If someone, for example, tells you that palm trees grow near the north pole you would dismiss it…

6. Limitations to observations
But there are limitations to our observations so we cannot just immediately dismiss every claim that conflicts with them
For example, one’s observations can be unreliable:
Due to environmental conditions such as poor lighting, or too much noise.
If one is distracted or emotionally upset.
When one’s senses are impaired, for instance when one is drowsy.
When instruments such as eyeglasses aren’t working correctly.

7. Other hindrances to good observation
Our observations can be colored and influenced by our own attitudes, beliefs, hopes, biases, personal interests, fears and expectations.
For example, if you are infatuated with someone, everything he or she does seems wonderful.
In such cases the observations we make aren’t objective. They aren’t correct because they are colored by how we feel.
Our own memory can hinder our observations.
Unless one is able to record her own observations...

8. The Credibility of sources
A source is a person or place from whom one has obtained some information.
A source can either lack or have credibility.
For example, a bird expert is a credible source for the claim that ducks mate for life.
The credibility of a source comes in degrees.
For example, a habitual liar is much less credible than a person caught making her first lie...

9. What is irrelevant to judging the credibility of a source?
We sometimes use irrelevant considerations in judging someone’s credibility:
For example:
Physical characteristics such as eye color or height.
Certain body gestures and postures, for example maintaining eye contact, sweating and laughing nervously.
Gender, age, ethnicity, accent and mannerisms.
The clothes one wears.

10. When a source isn’t credible
A source can lack credibility because:
She lacks the requisite knowledge
She isn’t truthful,
She isn’t accurate.
Maybe the source has a faulty memory or she wasn't able to make accurate observations
She isn’t objective
Maybe the source is biased or opinionated or emotional or conflicted about a subject.

11. Biases
To have a bias toward a person, place or thing is to favor that person, place or thing over others.
We must beware of a source’s biases
When we are reporting on someone we have a bias toward, we may unconsciously accentuate the positives and understate the negatives.
If you think a source is biased it is best to be a bit cautious and skeptical before accepting that source’s claims

12. What matters when judging credibility?
There are several factors that matter when judging a source’s credibility:
Education: formal education, most notably, counts in someone’s favor. The key is possession of degrees from established institutions of learning.
Experience: A person’s credibility is raised if she has experience in both quantity and quality which is relevant to the claim being made.

13. Judging the Credibility of a source
Accomplishments: A person’s accomplishments can raise her credibility when those accomplishments are related to the claim in question.
Reputation: reputation matters when it is reputation in a field related to the claim in question.