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Justification via Other People’s Beliefs

We may justify our beliefs using intuition, reason, emotion, and our senses.

We may also justify our beliefs using other people’s beliefs. For example, someone may believe sunlight originates from nuclear reactions because their teacher believes it. Alternatively, one could listen to why their teacher believes sunlight originates from nuclear reactions, study the requisite math and physics, and justify the same belief directly.

In the first case, we justify our belief using another’s belief. In the second case, we adopt another’s justification for ourselves, without relying on their belief.

Often, we combine these approaches; we may know enough nuclear physics to accept our teacher’s opinion, and so we justify our belief partially with our knowledge and reasoning and partly with our teacher’s belief.

There are two problems with justifying our beliefs using other people’s beliefs:

  1. The other person may be lying.
  2. The other person may be wrong.

Given these problems, when is it appropriate to justify our beliefs using other’s beliefs?

Some beliefs can only be justified via other’s beliefs. Beliefs that prophets have had religious revelations fall into this category. For example, a prophet says that God wants you to stop going on expensive vacations and to donate to the poor. You can only justify your belief in the prophet by believing what the prophet says; you must believe that they are not deceiving you and they are not mistaken. Beliefs about historical events can only be justified via other’s beliefs because we are not present to see the event ourself. For example, your Uncle tells you that your great great grandfather had Parkinson’s disease; nobody else in the family was aware of this. Your belief that you have a family history of Parkinson’s is justified via your Uncle’s belief.

Other beliefs, while possibly to justify on our own, would require an infeasible amount of resources for us to do so. For example, the experimental evidence for our theory of nuclear reactions in the sun would be difficult for me to reproduce because the theory is complex and the experiments needed to validate it are expensive.

Many beliefs can be justified on our own, but we do not have the interest, time, or ability to do so. For example, I believe that Australia exists although I have never visited.

Of course, some beliefs are more important than others. It would be wise to allocate our limited resources into justifying our most important beliefs on our own as much as possible. And, if we must resort to justification via other’s beliefs, we should take the time to understand the other person’s justification, and consider if they have ulterior motives. This way we may avoid the first problem, but we can not completely avoid the second problem, because we may be mistaken ourself.